(not do anything about it, but just complain about it)

What do you mean? What is she supposed to do about it, go back in time and stop him from cheating? People get cheated on, men and women alike, normal people mourn for awhile and get the fuck over it. Also, why are you just automatically assuming she'll get cheated on? That's some revenge fantasy bullshit, right there.

...she's going to call him back up really sweet and caring and lead him on for as long as she can get an ego-stroke while he listens to her problems.

Or maybe she's calling him up because she thinks he's an actual friend who's willing to listen to her problems instead of just wanting to get in her pants, but you're right, she's giving you him too much credit.

Oh, and then he develops feelings for her while she's leading him on and calling him at all hours of the night to talk?

Any guy who develops feelings for a girl over phone calls (especially ones that are clearly friendly in-nature) is just showing how desperate he is.

Yep, he's an asshole trying to take advantage.

Maybe she just wasn't ready for someone else to make a move? People need time to recover from getting their heart broken, it doesn't just happen overnight.

Until the next time she wants to cry about her bf who's banging some chick he just met and wants him to come over at midnight to "take care of her".

If her boyfriends keep cheating on her, then that should tell you there's something wrong with her.

But he doesn't know any better when she's leading him on for positive attention.

At this point, I think what you mean by "leading on" might just be "speaking."

She's getting the bf experience from him...

Sure, the "bf experience." Without all of the romance, affection, and teamwork that goes into actually having a boyfriend. Hey, wait a minute, that's a friendship.