How do I deal with my depression?

I'm 15 and I'm suffering from depression. A lot has happened to me in the past and I don't know why things suddenly changed. I started acting different after my parents separated but the was years ago. Last year I started cutting myself. My dad found out and I stopped for awhile. Others things happened that brought the depression back on and I cut myself again. My dad doesn't know about this last time. I've tried really hard to stop cutting for good but every time something bad happens my mind automatically think of it. I had a bad break up earlier this year and instead or cutting I took drugs and alcohol. I've stopped that as well. I use to not care what other people thought of me but now I do. I worry about my weight and watch what I eat. Sometimes I only eat one meal a day. I try not to let it bother me either and I've been trying to lose weight in a healthy way by watching what I eat. I've been really happy lately with by boyfriend and everything but recently my depression kicked in. I don't want to talk to anyone and I feel lifeless. I've thought of cutting but then I realize it won't do anything but give me another scar to look at. It's been months since I last cut and I don't want to start again. I don't want to hurt my body anymore so how do I overcome my depression in a healthy way?