Hi Cathy, thanks for submitting your story. I had a look at it and enjoyed it, it was a good read!
As for your questions, rather than answer them one by one, I'm going to split this into sections as my thoughts have a tendency to wander. So here goes:
For English being your third language, this is pretty excellent! Nothing remotely approaching a massacre, but maybe some things to consider:
Some of your sentences can get a little wordy and unwieldy. For example, in the first paragraph: "I wrote on the card, my fingers trembling of their own accord as the memories of the past ten days flickered in my mind and the prospect of what lies ahead slapped me magnificently on both cheeks, clearing my head of any other thought, dream or desire." (Long sentences may be appropriate in certain contexts, but when it's right at the beginning of the story it sort of sets an uncomfortable precedent!) Other examples: "her tousled short hair dancing with the wind and playfully caressing her face with a few dawn rays shimmering on the blonde strands" - that's a lot of information for one sentence.
I think it's also worth looking at some of your word choices, such as in "considering the schism between where I had been..." - "schism" makes it more obvious that i'm reading a story; it seems like a deliberately selected word rather than a natural one, and as a result the sentence doesn't flow. You could try something like "comparing where I had been..."? Another example: "I smiled again, knowing I had already done those, with her" - that's a bit of an awkward way of phrasing it. Try to think of a more natural way to deliver the same information - for example, "I smiled, remembering". That implies they've already done those things, but it's more subtle than just telling the reader.
In fact, I think there are quite a few cases where there's unnecessary "telling", or unnecessary information that detracts from the scene. For example, "I shouted to her, defying the accepted norms a woman's voice should observe" - think about whether that last bit really adds anything to the sentence. What does the reader gain from it? Does it properly deliver useful information, does it help to establish a mood or atmosphere? Or does it just confuse things, and run the risk of distracting the reader with extraneous thoughts? I know when I read that, I couldn't help thinking about just what the "accepted norm" was, and it took a few seconds before I got back to reading the story. I know that could be just me, but I think you have to weigh sentences like this in the balance, and anything that tips the scales should be cut. Some other examples:
""Oh, I'm sorry," I answered, quite embarrassed by my distraction."
"I almost choked on my ... wait, I wasn't chewing anything then to choke on it, and yet it still felt like I couldn't breathe or swallow."
""You know me better than to accuse me of that," I flipped the guilt ball back in her court." - that description takes what should be an honest statement of anger and hurt, and turns it into a flippant tennis reference.
"To be completely honest with you, it was also meant" - consider removing the "you" references to the reader. I don't think that's always inappropriate, but in this case I think the reader's focus should be on the story, and speaking to the reader like that tends to break the immersion I feel. It sort of spoils the whole voyeuristic mood of reading, although maybe that's me overthinking it a little.
"For a brief second she was terrified, then she seemed to understand that I was only enjoying the view" - a small thing here, but I feel you should avoid describing other characters' feelings that way. You could say for example, "For a brief second she looked terrified," because that's what the narrator would see - the narrator wouldn't know
what the other was feeling, only what the other looked like she was feeling - if you see what I mean.
So it looks like the whole set up of the backwards story depends in no small part on the reader wanting to know the significance of the sentence "I know where your tongue has been" - that's the mystery that promises to be revealed, one of the hooks that's meant to draw the reader in, as established in the second paragraph (and the title, I guess). As a hook to pull me into the story it works - but only initially, as I think that sentence becomes a bit overused. It appears at the beginning of each section, and often within sections as well, and such extensive repetition runs the risk of rendering that sentence meaningless. When the narrator writes it on the card at the beginning she acts as though there's a tremendous weight to it. Would something that has such a stirring meaning to both of them really be used so often and so casually? I think several instances of that sentence can be removed without harming the flow of the story, which would make it easier for the reader to see just when that sentence begins to take on its deeper meaning for them.
In general I don't think it's really necessary to establish such a robust timeline - I feel like you'd want the reader to be more concerned with the characters and their developing relationship, rather than with trying to work out exactly how many days have passed between sections. I think as long as there are links between sections, that's enough. So as long as the second section has her mouthing "tomorrow" and the first section references it as yesterday, we don't need to know that nine days have passed since they first met. It just seems to me to get a bit repetitive: in the first section you say they met ten days ago, then in the next section you say they met nine days ago, in the third section you say they met eight days ago, etc. I don't think that precise chronology needs to be in the forefront of the reader's mind; that space should be reserved for the characters. Not to mention it can get a bit awkward trying to work in the exact number - for example in the third section the narrator thinks "Hadn't these eight days meant anything to her" when "Hadn't this past week meant anything to her" would be more natural. Honestly, I was impressed as I read this at all the ways the different sections linked together. I think you've done a great job with all the subtle connections as it is, and this focus on establishing the precise timeline I feel does more harm than good - it draws undue attention to something that should be subtle, should be in the background, like a secret reward for anyone who bothers to look.
Initially I thought they met as the result of some workplace bet (hence her surprise when comparing where she is now with "where she had been"), that resulted in one of them being fired (hence the "I'll miss working with you" in the second paragraph). But I didn't know what the "work" was until they were having coffee in the morning and talking about "he focuses on hedonism and complicity".
Eroticism... well, I should mention first of all that I don't find myself particularly drawn to lesbian erotica. That said, though, I couldn't help feeling that parts of this were a little over-described. Like the scene where sweat and saliva "melt into one fascinating transparent mix". I do think some of the descriptions were good - "Ah, I'd given up on trying to understand my reactions to her. My own body was a foreign land to me..." is one that stood out for me - but some of the others seemed a little excessive. As I said, I'm not the best person to comment on this, so I'll leave it at that.
I didn't mind at all that the characters don't get names or comprehensive descriptions - it doesn't get confusing (since there's only two of them, "I" and "she"). I kept a look out for any situation where a name would be more natural than the lack of a name, but nothing really jumped out at me - well maybe one small case, where "Jimmy agreed, and Carmen nodded along", and immediately after, "I turned my head towards her". Normally that would mean she turned towards Carmen, so here's an example of when a name would be natural and leaving out the name feels a little forced.
I do think, though, that you could do with a little more description of the setting. The rooftop scene, for example - that's a classic, two lovers on a rooftop at dawn, but that setting didn't really contribute as much as I feel it could have. Also the restaurant scene - when the scene began I had no idea whether they were sitting at the same table, what kind of restaurant they were in, whether it was crowded... these things aren't essential, but a couple of quick sentences to help draw the scene would be helpful. And it does tie in to the characters - if they're in a posh restaurant there'd be a bit more embarrassment; if it was crowded she might be a bit more cautious than if they were in a corner table of a mostly-empty restaurant. (Personally, I wasn't really convinced by the logistics of this scene. It takes less than a second to pick up a phone, and in my experience if someone drops a phone and goes under the table everyone looks, and moves their chairs backward, especially if it's a small group of friends, and especially if the dropped phone interrupts a conversation that everyone's eager to get back to. Also, it's hard to imagine how she couldn't reach the phone if she physically went under
the table - if there are only four of them, how large could the table be? - unless it somehow rolled some distance away. And putting a finger in the sauce? But that's just me, and from a character point of view I think the scene was quite effective.)
As for the characters themselves: as I see it the main thing you needed to convince your readers was that this depth of emotional connection that the characters display at the "beginning" (narratively) has legitimately developed over the course of the short period they've known each other. I guess this is part of the challenge of writing something backwards, and it's also a unique narrative opportunity - kind of an "okay, you've showed me how close they are, now convince me this is real". Sort of like a magic trick in reverse ("okay, you've told me the rabbit came from the hat, now convince me it actually did"). In that sense, as I see it, it's the fidelity of the characters that must justify the reverse chronology of the narrative. Here's where the problem is for me.
I think in some cases the main character runs through some seemingly contradictory emotional states. One example is the fourth section, where they're in the restaurant with her two friends. The narrator has just been thinking how her other is "getting her revenge over every second I had teased her in public" - and then she smiles and thinks "I would have done the same thing, if I was her". I guess it's a small thing, but it just doesn't seem to really fit. That doesn't seem like a usual response - especially given how emotionally drained the narrator is from the depth of her feelings, from the uncertainty of not knowing how the other feels about her.
I like the back and forth between them - how in some sections the narrator is the one being kneaded, and in other sections she's the one being needed (if you'll forgive the attempted pun). I like that there's a game they play but there's always an undercurrent of deep emotion behind it, although I do think the narrator has a tendency to over-describe how she's feeling (such as "my blood rushed like a mad race driver between my cheeks and my lower abdomen, thumping against my ear and heart on the way"). Again, however, I feel that the emotional states of the characters don't carry so well between sections. For instance, in the restaurant scene the narrator begins with feeling like she's "tearing down and rotting inside", whereas in the scene chronologically before that (narratively after), she leaves feeling self-assured and in-control. I know you specifically say "It was hard to believe...that I felt so completely at loss now that she had ignored me for the past [day]", but that's not enough to convince me that it would actually happen. Why the sudden shift to desperation?
I also like the numerous hints to "previous" events, but I think it's worth considering how integral these are to the characters' actions. By which I mean - in each scene, how much of what they do and say is dependent on things the reader doesn't yet know? I think there needs to be a balance here: if all
of their actions depend on things we don't know, then the whole scene comes across as very flat and meaningless. So the ideal is that each scene should give us "current" insight into the characters, while at the same time promising further insight once we know what happened "two days ago" (for example). Personally, I feel there was a bit too much dependence on things that would only be revealed later on in the narrative.
So in summary: there are parts of this backwards narrative that I think work really well - the hints in one scene that pay off later on in the story make it interesting and rewarding to read. And the scene where they're having their first go together in front of the camera is intense and meaningful in this context. But I feel it gets a little gimmicky with the repetition of "where your tongue has been", and overall, I have to say in my opinion the characters don't quite carry through enough for me to say that the backwards narrative is justified. (I'm not saying the characters themselves are bad or unconvincing - just that the backwards narrative doesn't quite do justice to their character development.) I don't mean to end on a sour note - this was a well-written story and, as I said, it was really fun to pick out the little details that fit together between the scenes - but I have to be honest. For me, this is a character piece, and I feel the development of the characters would be better served with a more conventional flashback (begin with the scene at the florist, then let the rest of the story play out chronologically and end at the florist again). That way the initial mystery is not so much "when was the sentence "I know where your tongue has been" first used?", but "when did that sentence take on such a deeply significant meaning for them?". You could definitely keep the reader's interest without resorting to the reverse chronology - just let the characters and their intimate connection speak for itself as it grows and develops. Instead of ending with a tender recollection of their first meeting (as the story is now), you could end on a tender image of their future together.
Still, this is only my opinion
Hope all this is helpful in some way, and all the best for your future writerly endeavours!