I ended a ten year friendship about four years ago because I couldn't handle staying in touch with my best friend who was killing himself with alcohol. We were talking on the phone everyday (I had moved away) and I could see it getting worse.
One of the reasons I quit drinking about three weeks ago is because I finally got the phone call that he was dying. He never wanted any help from anyone, and still doesn't. I don't know which was harder: watching him slowly kill himself, or ending the friendship. Either way, it wasn't my choice, it was his.
I'm on the fence about whether or not to contact him in the last few months he has left as we've now been estranged for quite some time. But it had a huge effect on me in that I was seeing myself starting to head down the same road he did. However, I did something about it. Yet, I can tell you from experience, no one could have helped him and no one could have helped me when I was in it. It truly has to come from deep within.
I hope you find peace with it either way.