Kafoo-
I am not sure where you go to school (what country etc) but generally if you are having problems (addiction, Depression, etc) schools will sign a waiver for you to be able to complete the class at a later date without getting a failing mark for the current class you are in.
When i was in college I had a HUGE bout of depression and went on a 300+ day binge. I was able to salvage a couple of my classes, but the ones I couldn't i got a written letter from my psychologist confirming my situation. I ended up having to go an extra semester, but I still graduated. I would suggest trying to use any resources available on campus (not sure what type of college you go to) to help. I know at my college we had tons of AA and other student services to help people suffering from addiction. I was just too dumb to take advantage of them.