I’ve been feeling so depressed lately.

I do not know what to do anymore. I do not want to kill myself, but I am just waiting for death. I am 18 and a male.
I have always been a little depressed. It all started when my grandmother passed away when I was 14. I felt like crap, I did not want to live anymore. I cried for days. The only solution I found was drugs. I felt too embarrassed to talk to my family about it. On top of that, my parents were getting a divorce at the time. I felt so much pain. Drugs were the only thing that rid me of my problems, at least for a while.
After about a year I was feeling better. By that time I was hooked on drugs though. I did not do them to relieve my pain anymore, I was just hooked. I tried letting go, but after a while of being without drugs, I would feel like all my problems would come back.
When I was 16, my mom moved to Canada with her boyfriend and left me here in the U.S. That just tore my heart. I felt so depressed that I started doing ‘harder’ drugs like Vicodin, Oxycontin, and Dextromethorphan. At 17 I was over this, but then like before, I was hooked to these drugs again.
Recently, I was in a relationship with a girl who I fell in love with last year. I thought she was the ‘one’. We had a very good relationship. I loved her. During the time I was with her, I was doing drugs. She still loved me even though she knew about my habit. She said she would be with me no matter what. Sometimes when I would go to her house, I would be so drugged up that I would pass out. I would wake up and she would be holding me and crying. I would always feel so bad and like an idiot for doing that, but I still continued to do it. Eventually she could not take it anymore and begged me, crying, to stop all drugs. I agreed, but she let me keep drinking. It was the hardest thing I ever had to do, but I did it because I knew she loved me and I loved her. The end of our relationship came when I messed up like never before. I went to a party with my sister and without my girlfriend (at the time). I got so drunk I ended up having sex with another girl. I was so drunk I ended up texting her about it. She said there, I broke her heart and said she never wanted to see or talk to me ever again. It was not until the next day that I realized what I had done. I messed up badly. I felt so horrible. I cried. Begged her for forgiveness. She cried, but in the end she said I hurt her too much and said to leave her alone. Last week, I asked her if we could at least be friends. She agreed. We have a good friendship going on so far. I asked her over a text if she ever thought she could forgive me for what I did and if maybe we could get back together. She said no.
I have been feeling so depressed. I cannot stand knowing that we will not be together anymore. Last week, I began doing drugs again. Now, when I am on them I feel so good and when I am off them I feel so terrible. Other things that are bothering me are that I am close to graduating from high school, hopefully. I have really low grades but just enough to graduate. The thing is I still have some big projects for some classes and I have been procrastinating. I have always been a procrastinator, I do not know why, but I know it’s bad. My mother will be flying here with the hope of seeing me graduate on stage. My father is feeling the same way. I know that if I do not graduate it will be so devastating for my parents and my entire family. If I see them like that, I do not know what I will do. I would feel so much guilt that I might end up hating myself even more or even hurting myself.