I'm depressed and it's over a guy, help?

I can't get over how bad this guy treated me, he just used me. But now I'm so depressed over it. I have so many things in my life that I should be happy about like graduating high school, and having people who love me. But I can't enjoy that from thinking of an emotionally abusive jerk. Help me, what should I do, how long will I stay this way