How to cope with a farther who want help himself???

My mental health is pretty good right now. However, due my 11 month old son and covid we're living at my dad's house. About 10 years ago my mom cheated on him after 25 years of marriage and tossed my dad aside like nothing. Understandably it left him a deep depression.

I'm not saying he should suck it up and forget it ever happened. I mean he's stuck in the past and blames himself. What makes it worse is that my mom wants to be "friends" with him. She has even came to his house with her new husband and expected it to be fine. In which my dad was okay with on the service at least.

Every time my mom sends him a message, calls him, or tags him in social media my farther is depressed, angry, and drinks more.

I've approached him several times about his mental health. The most recent time he broke down crying and told me he is incredibly lonely. Which after 25 years of marriage who can blame him.

I have pleaded with him to see a therapist and a psychiatrist. Event joining a divorced group. But he refuses to seek help. He's old school and doesn't think a man should express any sadness or hardship. So he expresses it by being a A-hole to everyone in his life except my son. He also drinks the equivalent of 14 beers everyday after work drowning his sorrows.

I really want to help him, but I can't risk my mental health, my wife's and especially not my sons. How do I come to terms that he is most likely never going to seek help and drink himself into a early grave???

I don’t have any advice, but I’m very sorry you’re going through this, and sorry for what happened to your dad. Being betrayed like that really does a number on most people and it’s incredibly tough to move on, even for most people who eventually made it to a happier place, psychologically speaking.
The best thing for your dad to do, though I doubt he would, is to break off contact with your mum and block her on all his social media etc. That would be a good first step towards him healing. If he has any hobbies or interests would he join a group of some kind so he could meet other people?

I agree with RoxanneToto that total blocking of ex is a necessary step.

I would love for him yo severe all communication from my mom. I failed to mention this in my original post, but my mom is stringing him along. She has visited our house just to see our son during the day and to flirt with my dad at night. She is giving him emotional whiplash.

I would love to help my dad, but I’m afraid I’m going to have to accept his fate.

The inference was there, and I’m very sorry that she’s doing that to him.
I follow a blog that’s basically all about getting your own life back after infidelity (it’s not about reconciliation or saving the marriage; in the vast majority of cases it turns out to be a waste of time). I’ll post the link because there may be some useful resources in it for you, and possibly your dad; there are several years worth of posts now, but you can send the blog owner a message. Most posts are responses to letters she publishes, and she has a book as well.
ChumpLady.com - Leave a cheater, gain a life!
I hope you can help your dad, it sounds like he’s really hurting and confused right now, understably.

Thank you for your suggestions everyone.