tl;dr: have a friend who has historically always been mad when his friends got a gf/wife. He acts like he's 15 years old and saying "bros before hoes" still. He calls me and other friends a yuppie or breeder, and he thinks crosswalks are authoritarian so he has to always be a "rebel" and make it seem like he has the most unique viewpoint in the world. He doesn't change anything about himself, and he's stubbornly proud of having "no filter." This has caused every wife/gf of his friends to not like him. He will never be invited to any kind of social event because he will say stupid shit. Like, nobody has to be a rabid commie all the fucking time. Him and my gf got into a huge fight because he always talks like an asshole, and i live with my gf, so he doesnt come to my house at all because he'll say some shit. He still brings up this fight when im around him, and it's like get the fuck over it. I basically don't share anything about my life that involves my partner now, because he'll say something fucking stupid about her. He also begins a lot of sentences with "well" or "actually" which is never helpful. He literally can't admin when he is wrong, even about the simplest shit.
This really all seemed to get worse once I started my current long term relationship, and then it got way worse when my gf got sick of his shitty attitude and how he treats everyone like an asshole. He literally just can't be chill at all. No leftist(or similar) should be ranting constantly about every single injustice during every single social situation. That is exhausting to be around, and there is a time and place for it, but there has to be an ability to switch that shit off.
Finding and keeping relationships requires changing yourself just a bit, and making compromises, and it's now become apparent he isn't capable of that.
related question: have you ever dumped a long time friend? This is all a somewhat recent change, like the past 3-4 years, and it really seems to be because im in a relationship like most of our friend group, so now he's totally alone. Ive heard him say he's in therapy but i have to wonder if that's true, because it clearly isn't working. I'm annoyed by him but I pity him too because he can't fucking change for anybody at all.
Sounds like your (ex) friend needs help and the type that you can't provide. From the examples you've given they're probably having some shit going on, whatever it is, and it may have been an entire life of shit, I don't know. Either way, as shitty as it feels, cutting off people at a certain point is for the best for you and for them if they get the message that everyone is sick of their shit.
My ex-gf's dad (yes, her dad. A guy in his 40s or so at the time) was a complete disaster, similar-sounding to this friend. When we got together in our early 20s her parents were together and about 8 years later by the time we ended things her parents were divorced. They divorced when she was an adult which... seems uncommon? But I dunno. It was 100% on him too as far as making no effort. Kinda like your friend. He ignored all chores and responsibilities, would go drinking with his buddies all the time, drove around drunk, went to jail at some point for stealing tax money (long story). And now as far as I know he doesn't speak to his children and his ex-wife, somewhat understandably, would like to see him dead before she speaks to him. He was a complete dickhead throughout all of the shit. Refused to sign papers for a divorce he instigated by cheating and all the other shit. Complete bag of shit.
Yet I have to assume that he had something inside of him, whatever it was, eating his mind from the inside. I felt bad for him on a human level because there's no way a person can be married for 20 years+ and just cut off their son and daughter and now-ex-wife without causing some serious trauma and being started by something seriously wrong in their outlook on life. Nearly suicidal, I would think. I mean he practically destroyed everything he had, the family he had, and his daughter and son definitely loved him as a father in many ways. I know from years with my ex and her brother.
It's impossible to know why people act the way they do, like teenagers in adult bodies. They probably don't even know themselves I imagine. I think in the end all you can do at a certain point once it's damaging your life is tell them as straight as you can to seek help from professionals and you're not going to be around anymore for the bullshit.
As for the final question, yes. Besides the above-mentioned guy, who was quite friendly with me before and attempted to be afterwards (like nothing happened...), you know sometimes you just get sick of people or sometimes they do something beyond the pale and beyond the scope of morality that you can never forgive them. I've completely cut off people for petty reasons more as a mental health break for myself. I've also cut off people, one guy specifically I knew from high school and onward into our 20s, for doing egregious acts that I'll spare everyone from reading and myself from having to type. I cut that one off because he did it to my friend and I'm not like an overly-angry internet tough guy type or even real life tough guy type, but I just knew, and have had many dreams about it unfortunately, that if I ever saw him after hearing about the stuff he did that I'd want to smash his face into pavement. So, I had to just block every possible way for him contact me and it's been ok for over a decade now. I dunno, it sucks. You trust people, you like them, you spend time with them, and when they're around you maybe they're decent. When you learn how they really are around others and you can kind of step back and see that it was an act to an extent around you, it's a betrayal for sure. It sucks to know you've been manipulated into liking someone who could do these types of things. And it sucks knowing they probably don't give a shit. I mean, maybe he does. I don't know. I'm still too angry over the situation to really analyze it and feel bad for him in any capacity or question his motives at all. I probably never will. Shit just sucks sometimes and I'm not sure there's anything we can do besides cope how we can, get help if we need it, and try our best to move on and find people who don't suck.