We first started when I was 14 and she was 13, just to try it, but we kept doing it. Now I'm 18 and she's 17 and we still go at it. Its just a sexual thing, like f*ck-buddies, and we've both had boyfriends and girlfriends while keeping this relationship. We've even had a three-way with an ex of mine. But now she's getting really possessive and I'm getting kind of worried. I've told her I want to stop, but she gets really depressed when we do, and I've had to talk her out of suicide twice. I have no idea what to do.