How do you get over your oneitis? I've been depressed

Realize you are lacking in direction and that you need to find it. Then use that need to find things you are or can see yourself becoming passionate about (it doesn't happen immediately for everything). Then work to build skills pertaining to every area that interests you.

After about two or three years of this, your oneitis should be, for the most part, cured. If you're like me, it's likely you're still gonna see that girl in your dreams from time to time (esp. if it was a long relationship) if you haven't really found anyone else, but that's just your subconscious fuckin' with ya. Ignore it and focus on making the best of your situation going forward, and don't look back.