WHY? I used to be that way. But I've been single for all of 2008, by choice. It's a lot more enjoyable and less stressful.
I've had the misfortune of dating two unstable girls, but genuinely unstable. Not in the "all bitches are unstable, lol" way, but, you know, unstable. One because her mom had just been diagnosed with terminal cancer, the other was just manipulative to her friends and made terrible choices all around. Nevertheless, there are a lot of girls around, and I'm sure that a lot of them are basically, like you and I, stable, normal people. I just think that relationships are all about give and take, but as long as you can play your cards right and read people well, then you shouldn't step on feet all that much.
But as to why I want to be involved? Part of being in a new city. I don't have a lot of friends, not really too many opportunities to meet people. I'm in school, but whatever. I'm very charismatic and get people to open up to me and be legitimately attracted to me. I'm a great conversationalist. But with that, I invest a lot of myself into my relationships, platonic or not. I enjoy the company of people, and I have a dick that likes girls. It seems to go hand in hand. I don't care if you want to fuck every girl on the block, that's your choice and if you can do it, power to you. I'm more into bonds and steady, strong relationships rather than just investing effort into just hooking up with someone. Believe me, I've hooked up with a good number of girls and then didn't pursue anything after that, but I find myself just a little more tuned to having bonds with people. As any of my friends will tell you, I was great friends with them day one.
So, that's why.