Are you going to Al-anon or getting therapy? I highly recommend getting some help, it was a life saver for me.
In addition I just don't answer her calls, she can leave a voice mail or email me if it is important. I only listen to / read them because we are still married and have financial things that sometimes need to be taken care of. Once we are divorced, just started the process, I will block her phone and mark her email address as spam.
If I didn't answer the calls and just listened to the voice mails I gave myself some time to think about whether or not I really wanted to respond. I found it much easier to deal with when I wasn't directly involved in talking to her.
As for his health, well it's his health not yours. You didn't cause it, you can't control it and you can't cure it. Give him the dignity of living his own life however he chooses to.
I know this is a really hard thing to do but trust me, it gets so much better the more you remove yourself from direct contact.
Another way to stop dwelling on him is to focus on yourself and your future. I have been spending time the last couple of months thinking about what I would really like to be doing in the future, kind of a what do I want to be when I grow up. At 58 you'd think I had that answered already wouldn't ya?
Your friend,