I wasn't gonna make this comment about me, but..

Maybe you are too young to have a serious relationship.

This scares me as well, I got into a relationship with my girlfriend when we were 15, now I'm almost 18. I love her a ton and I don't see any problem with our relationship and I really don't want it to end, but we still have to go to university and we probably won't see each other much for a few years. It worked out for my cousin though, he's in a relationship for like 8 years through uni and a bit of high school. I just hope it works out for us too. My situation isn't as OP's, though, I don't get the urge to go with other women or such things.