Family drama. i can't take it. help, please!?

so i'm 22 and in college right now... i work at a department store, but til im out of college i'm living at home. my parents are divorced, live with my mom, sister lives in another city. they divorced in 01. my dad has caused a lot of crap...he was arrested for domestic violence, he was an alcoholic, made a lot of mistakes etc. hadnt spoke to him in years. if he called me at random times over the yrs and i'd talk to him, my sis and mom would ALWAYS accuse me of telling him stuff..and it was SOO friggin frustrated b/c i REALLY didn't. i'd talk for like 3 minutes. well my grandma, dad's mom, called me this yr, paid for my cell #. then my dad started. i was hesitant at first.. but over time.. he's livin with his fiancee trying to get the divorce finalized with my mom. my sister wont talk to him. he emailed her and apologized, etc, she doesnt want anything to do with him. me--i am talking to him..but mostly bc i dont want regrets later on. he says he's sick... not gonna die sick, but needs