Refer to title.
Sounds to me like you're in love. You pretty much feel crumby when you're not around that special person, you don't want to waste a moment of your life without them. It's all due to brain chemicals (ones that I don't know much about yet), it's addiction.
The way I see it, everyone has a void they need to fill. Some have a tiny void, and it's not a big part of their life. Some have larger voids, and they turn to an act that results in a desired feeling (sexual release, security, or to some degree, ecstasy). Thus they engage in compulsive action (habit) or by yearning for something to fill that void, and it dictates their level of happiness. You need to feel that chemical to feel good.
I have known a lot of people with a lot of habits, and I believe that you can never truly get rid of that need, you can only change the method through which you fill it. Short of prescription drugs, of course.
Sounds to me like you need to be with someone you love. Do you find that you go through lovers fast?