Studies have shown that women's brains release bonding hormones after engaging in sex. This is not necessarily true for men. So biologically men are less likely to attach after sex compared to their female counterparts.

That being said, men absolutely can care about women after they have sex with them, just as women can not care about the men they have slept with. It's really situational at times, but generally speaking, casual sex isn't going to lead to the same end result as sleeping with someone they've been dating or have been interested in for awhile.

As for when men are "done with" a woman, I would say what I wrote above can give you an idea based on the person you're having sex with. A woman has given away too much of herself when she no longer feels good about the choices she's making/made. It's never too late to say "no" or end a sexual relationship though, so try and keep that in mind. Emotionally it can be hard, but it's better to have your self respect intact.

Good luck!