I kept a bridge between my ex and I while my kids were growing up for their sake. I've known him since I was 14, so I truly do wish the best for him, but he has taken advantage of that at every turn. Once the kids turned 18, I basically stopped all communication. We simply see the world differently - he was severely abused as a child and then served in the military where his PTSD and behaviors only got worse.
His kids go to dinner with him every Sunday when he takes them out (I'm not sure he knows how to cook a real meal and eats out every day for his own meals), but other than that they don't really talk or associate with him. They say he embarrasses them even at the Sunday dinners because he needs attention, so he talks loudly in public about inappropriate topics.
I see him as a broken man who can't be helped. He's supposedly been in therapy for the past three years, but as far as I can tell (and I've talked to him directly about this topic), he uses that time to complain about his circumstances and play the victim. He definitely had a rough start (his mom hated him and he had to be removed from her home due to her severe physical abuse), and he hasn't been able to heal, so I pity him, but in the end he's never chosen to put his children first and they know it. And to kids, the why doesn't matter so much as the hurt he's caused them.
I'm fine to keep shouldering the "burden" of the kids. They're adults. They contribute to the household. And we are all very close. He is missing out on all that.