Time to Part

It's not rape because she indeed desires him (which is the problem to begin with), but that the part of him that she doesn't like about him isn't getting any better even with their compatibility. He isn't willing to better himself for her.

The story ends with him delivering an empty promise to her, which she understandably sees as lip service from him. This serves to reassure her that she's not wrong about wanting to leave him.

Their relationship is doomed, but she has enough appreciation for him to not throw it back at his face. His effort to console her sorrow is sincere, but he can't see that he's coming up short in her eyes. He thinks that his "fix" was enough to sway her, but it didn't.

Didn't really look like rape to me. Perhaps the girl was emotionally unsure of if she wanted to do it or not but it doesn't seem like she hated it or regretted it at the end and it looked like they parted on somewhat good terms.

You can argue that the ex didn't really have any right to initiate sex since they weren't in a relationship anymore but you could also look at as a man seeing his former partner in some emotional distress over this breakup and wanting to comfort for her.

He could also have an ulterior motive in wanting to getting back together with her but in this case I think its just two people who didn't function together as a couple but still have enough of an emotional connection to perform in one last act of sex for the wellbeing of the both of them.