Lisa Bonet's character just wanted to get laid. She didn't fall in love with Rob. She was still hung up on her last boyfriend, so moving in wasn't even an option. Rob's low self-esteem was related to large issues than just his break up. His whole life was in stagnation, and he needed to grow up. Laura had outgrown him, and he had some catching up to do.

I never read the book, but I think one shortfall of the film is that it doesn't really rationalize why she would move-in with a guy after immediately breaking up with Rob. I'd understand it if she had a one night stand with Ian, and even on the very night she walked out on Rob, but here she moves out and shacks up with a complete stranger before deciding to get to know him better and finally boink. I dunno, I just didn't relate to her thinking.

She didn't sleep with Ian/Ray until well after she moved out of Rob's apartment.
++++++
Love means never having to say you're ugly. - The Abominable Dr. Phibes

I known a guy, very close friend, a brother you may say.. he likes to play dumb when things like this happen, especially if a girl cheats on him while he was being serious.. he'll play along with her for a little while, like trying to be ultra nice; once he feels she is really in love with him again, like for real, then he cheats on her, with someone she knows or works, preferentially.. and he let the news spread naturally
Cold hearted bastard, but like they say, revenge is a dish best served cold
Here's another. There is this girl I know at college, really pretty girl.. party girl.. that does this regularly to one of the several guys she's seeing (she has like 3-4 regulars each year); she fvcks one or two while she's playing with the supposedly serious one
Now, call me old fashioned, but for me, this sounds a little bit crazy I think we are trading the essence of something that used to be beautiful for an endless mind game of who fvcks who first, who's the most cunning, who gets more medals.. while in the end, we are just hurting each other
Anyway, there is truth in this: be wise, know who you are dealing with, especially if you are in for a serious kind of thing.. if not, who cares, live and let die

I feel the same way, no self esteem. Anyway, you have it wrong, he didn't move outshe did. He should have just manned up, moved all her stuff into storage and changed the lock. She moves in with an older ponytail guy from upstairs? What, no girlfriends or family she can stay with? What she did (moving in with the guy from upstairs, calling, constantly showing up) and put him through was just cruel and showed that her only interest was in punishing him. Along with storing her stuff away from the apt. and changing the lock, he should have also refused/ignored all calls from her. Who in their right mind would want to continue a relationship with someone as vindictive and cruel as her? Obviously he had no problem meeting women and there are plenty more out there. I'm sure someone more compatible than her. This is obviously another "Chick flick" though so the male lead is going to be portrayed as the bad guy, at some point he'll roll over, and eventually take the girl back if she wants him. He will be the one to apologize for his actions but she won't. So sad!

Yes he deserved it, but as fast as she cheated means she was already thinking about it or she was simply acting out. He must have not been that great of a lover or she would not have left him for he ex.

Rob cheated on her so it serves him right.

Ya, that was pretty wack! That crosses the line for me. He was gross and it's too disrespectful, but then again he did cheat on her

Yeah, especially an older dude, with a pony tail. WTF

It's been awhile since I saw the movie, but in the book he had moved out of the apartment by the time Laura shacked up with him.