I am so sorry to hear you are having such a tough time. Losing your father when you were so young is devestating. I too am dealing with health issues and I have battled depression. I think talking to your doctor about getting on an antidepressant would be a great idea. I am on Effexor and it literally saved me. You go from feeling so sad and angry all the time to feeling normal again. Things that made you happy in the past can make you happy again. When you are depressed, it doesn't seem like you will ever be happy again. It is a very lonely feeling.
I also think talking to some kind of counselor or therapist would be really helpful. They could help you learn coping techniques for your fear of ending up like your father and help you with learning how to grieve in healthy way, instead of turning to drugs and alcohol.
Also, just sharing your story on here helps - makes you realize that you aren't alone at all! I know I feel better when I read others stories and when I share my own.
Hang in there - things are going to get better!!