Confused and Lonely

This may seem like a minor problem, and I'm hoping it will fix itself, but I've been hoping for a long time. I am a 22-year-old college student and I am a little tired of myself. I've suffered from debilitating anxiety ever since I started college. I've actually had to withdraw from school twice and come back home because I was so miserable being away. I don't see anything great happening to me in the future, as I am always down on myself and I have a habit of not being present. Still, one thing that I can't seem to understand about myself is my reluctance to open up to someone and have a real romantic relationship. I'll talk to guys when I go out, and I go on dates every once in a blue moon. I'm sure I'm not into girls, and I generally don't have trouble attracting guys, but I always feel that something is missing. There's never I spark. I've had really big crushes on a couple of guys before. I think I may have even fallen in love once. So I know what it feels like to fall in love and want someone really badly. Still, it feels like I'll never feel that way again and have the feeling be returned. I don't like the idea of casually hooking up with someone and waiting for a relationship to develop, as I'm not sexually experienced and don't want to start out that way. Maybe I'm just shy or scared of the opposite sex. What is my problem? Also, I go on asexual streaks where I have no sex drive at all, but there have definitely been times when I've had the exact opposite problem. I know that sounds kind of laughable, but bear with me. Can anyone relate to this, and have you overcome your relationship problem (or lack thereof)?