Why cant i enjoy life anymore?

I used to be very content in my life, I've never had it made or anything, but I remember just last year being happy, single, working three jobs just to pay the rent on my shitty house in the middle of the ghetto. Then I ever since I dated this chick for a couple weeks, its like I can't enjoy life without her. Nothing that used to make me happy does anymore, my friends and family aren't nearly as important to me as they used to be, and I keep holding on to this need to be with her. I really don't get it, I've lost all of my jobs, my house, and spend every day wallowing in self pity, and when I do get out I have to force myself to do so, whether it be going to the gym or to a party, and don't even mention looking for work, that's damn near impossible. What's going on with me? How do I get that spark back and enjoy life again? I'm tired of feeling all suicidal and stuff, its been five months and I'm still not getting better.