It's got. . .potential. Okay here's the cliffnotes version of why this got so radically passed over. You have a lot of authors, myself amongst them, that for the most part if I'm going to pick up a story from here to write (as opposed to helping you develop ideas, I'm always happy to be a sounding board) I want something short and sweet. Ideally that I can handle in two or three sittings tops. A multipart story that's going to involve a lot of build up and characterization just isn't going to do well generally for that reason.
This story is fairly well outlined though I thik you'd probably be better off with his girlfriend teasing him about the louder girl first. Especially if you take the "plunge" and make her well more a little chubby. As you have it (or I interpret it) You've got Loud and crazy porn star, Average girl, and no boobs girl. Well how bout you bump pornstar in favor of a little thicker but she doesn't have any issues so she'll just flaunt her natural and large breasts and the boy tries to hide his occasional gaze. No threesome there just some teasing maybe even some slutty role play (perhaps with a cheating scene at some point or at least the loud one asking why is having her pretend when she's right there) After that I'd probably follow your script. Though if he turned down the loud one earlier she's gonna make him earn it and if he didn't then he'll be intensifying the relationship with her at the same time his girlfriend and Mouse are. Still good outline.
I'd suggest you try to write it yourself there are lots of people here (not me in particular though if you only want some little bits I can do that) who will be more than happy to help you develop your writing skills if you think they are lacking. The good news here is that ultimately the good news is that if you write a longer story the readers tend to be much kinder. Mostly cus after four LIT pages which is I think 16 regular pages but don't quote me they would have quit if they didn't like your story.
Liar to 4est: Are you a cheese?