Dad killing himself...am I guilty?

In the past few months I have witnessed my dad drink his life away. Don't get me wrong he is a great father and has always been. He has worked his whole life to provide us with nothing but the best. The only problem is that he has a drinking problem. He comes home from work and drinks beer all evening. The worse part is that he has diabetes. He is no longer together with my mom but everytime they do speak she tells him how important it is for him to stop drinking but he wont listen. That is one of the reasons why she eventually left him and went back to Mexico. It kills me to see him do this to himself...but I cant help and wonder if one of the reasons is because of me. I use to be a great kid, all straight As through out high school, got into UIC with some scholarship money but then I gave up. I entered the party world and things have gone really bad since.
I feel that I have let him down in the worst way possible. I started drinking a lot, throwing parties in his house like crazy, crashed his car, got a DUI, and just recently in 2016 got locked away for a year. it is embarrassing to say the least but it probably was the worst and best thing that could have happened to me.
I was in jail and sentenced to Boot Camp. I was released in Feb 2017 and since then have kept the same job, have been working crazy over time hours and have set my priorities straight. I guess its better late than ever right? The one thing I cannot stop is smoking weed. It makes me feel so relaxed and makes me have a better outlook on life. How do I tell my dad to kick his addiction when I myself cannot stop mine? My brother has tried telling him to stop that he is harming himself and making us sad and worried along the way. his response is that it makes him happy and he isn't hurting anyone by drinking ... he says what we do (smoke weed ) is worse than what he does. Now what worries me the most is he has so many doctor appointments but never tells the doctors the truth. he tells them he only drinks socially ... and he refuses to let us go and speak to the doctor with him. At this point I feel helpless and guilty for everything I put him through. Am I just overthinking or could this be possible. Are my past actions killing him slowly? I guess I just wanted to put my thoughts out there and hope others can relate.