For some reason, people think that they're being "nice" as long as they're getting fucked over and/or used by someone.

That's not nice, that's just insecurity heh

If you find yourself in this situation over and over again, there's a good possibility you don't have the best self image, and you're relying on a woman who will accept you to feel better about yourself. There are PLENTY of "nice" people out there (both men and women) who can cut the manipulation thing out as soon as it starts.

My advice....take some time, I mean a LOT of time to think about WHAT it is, exactly, you are upset about. Once you find that, then think about why you're upset, what got you to that point, etc. You'll find the underlying issue, then you ask the same questions again. You'll continue to dig deeper and deeper into the issue, until you find your answer. I think it'd be good and healthy for you to do that and find the root of the problem before even thinking about getting involved with another woman.