What does it mean when two married people can't have a conversation without it becoming a screaming match?

My parents have been married for 30 years and are now at a point where they can't really talk without it becoming a fight. My father is 10yrs older rhan her and has failIng health. I have a half sister by my father, who is 12 years older than me. And apparently there is still ALOT of unresolved drama from before my time. My mother's 2 sisters have a strong dislike of my sister, again from past events which I know little of. And I believe my aunts fuel my mother's contempt.

My father drinks heavily and spends all of his spare time playing online poker. My mother spends literally hours on Facebook and I believe is addicted to food. So...in their own ways...they struggle with addiction.

Im exhausted from living around this. Its probably been this way my whole life...and now an adult...the effects of such a volatile environment are showing on me. I'm beginning to drink heavily myself. I have a very short temper. I feel that I'm virtually a ruined person. I can't afford to move out. I dont know what to do or worse...IF there is anything I even can do.