Players getting played

So that Christian K guy that I thought was another player, was actually an ok guy..he started seeing a girl a month ago, and just found out she was with other men behind his back. Hes devastated. So women do it too. Why do people treat people like that? Is it because of disturbed upbringings, or fear, or power? Its like you give everything to someone one, and they just kick you in the face. i know how the poor guy feels, god knows Ive been there often enough. Its one of the negative sides to being a nice person, you attract scum. Still at least I could spend some time comforting him, not all women are like that, I guess in the same way all men are not like that. But its hard to trust until you can be sure...