that sounds like a very difficult place to Be in..a challenging road ahead for all concerned.
you have a lot of compassion, and he’s lucky to have you, from what it sounds like he Seems too consumed in his own thoughts and problems Andy has forgotten, or put aside the work it takes to uphold a relationship with you... I get like that, Andy my problems are similar to his.
From my own thoughts, my mum eventually died of alcoholism I could nothing but watch it happen, it left me in dispair for 20 years, I know this doesn’t sound like a positive response, but perhaps it’s not going to be for him or his Dad, in the short term at least.
I guess what I’m saying is you can take that journey with him and do your best, (just don’t take on the load as he is possibly doing now) there does need to be a sense of Separating yourself from the darkness of his problems, let him turn back at you and seing you prosper with what you want out of life, he will see sunshine and maybe want to be a part of it..
does that make sense?