ISS, maybe and maybe not, but if you want a near-future space story with a healthy dose of feels and science, check out LoquiSordidaAdMe's Time to Breathe.
It's a bit long, at 6 Lit pages, but is worth the read.
Zero-G sex sounds intriguing, if you don't think about it too hard. But remember that NASA's ship for training astronauts to survive in zero-g is called "the Vomit Comet."
The place: ISS-3, the expanded station, a classic big purewhite donut whose slow spin produces one gravity at the outer ring and zero at the hub. Lovers pick nooks in the tunneled spokes at their desired G-level. (The spokes hold many fuck-nooks, of course, because LIT.)
The time: Near future, when somewhat humanoid ET aliens with implausible anatomies live in their own sector of ISS-3. Or maybe they just snuck in when nobody was looking.
The situation: Pick from any of a zillion space operas.
There were some ideas somewhere about elastic band strap on structure a couple could wear around them to help with the reactive forces in zero G, because otherwise it's just too much work to stay connected, if at all possible during powerful hip thrusts made. And then, body fluids flying around can be a hazard.
Such pesky realism aside, free floating sex is a hot fantasy. Perhaps it could be done underwater, but that adds other problems.
Now I'm just curious, how attempt of sex inside a zero G water tank would look like?