Personally, I always feel like I need to conserve my energy. Because for some reason, I don't have much of it. Or at least I think I don't, because simple social situations make me feel like I ran a marathon. It's probably because of my need to be alone. It is for this reason that having a relationship would be a bloody nightmare for me. I mean, I can't even have a face-to-face conversation with most people for over half an hour without feeling the need to be alone, and a girlfriend would be even more demanding than that. There's responsibilities that come with being in a relationship and... man, I really hate responsibilities. It's an immature-ass way of doing things, but hey.
I did have a girlfriend once. Or... could you call it a relationship, I wonder? It only lasted two weeks, after all. I'm pretty sure I, being the idiot I was at the time, just fell for her because of her looks. And it was probably the same on her end. But she turned out to be kind of a... well, you know, b-word once I got to know her better. Additionally, she was really really needy, and that's something I couldn't deal with even back then.
Since then, I haven't been on the look-out for a girlfriend again, and hopefully never will. It's just a pain.