I understand this, it's something I've had a problem with in the past. I was obsessed about getting this girl who wasn't into me to like me. It took a toll on my life for a good six months, I was miserable.

Basically what I did was try and recognize the thoughts every time I had them, realize they were irrational, and try and deal with them. Believe me, I know it's not as easy as it sounds. You just have to remember that you're the most important person in your life and nobody can give you self worth but yourself. Try and distract yourself with hobbies and start trying to better your life. If you throw yourself into something you love you'll be surprised how quickly your obsession goes away. It's good that you posted about it, getting it out is half the battle.