A very good friend of mine that i have known for almost a decade keeps doing this:
He's so sweet, he's a social butterfly, a GREAT friend, he's loyal and he's so kind. We have had some close mutual friends, but over all we ultimately have different groups of friends... but the fact that we also had a bunch of friends mutual between us made it fun when we planned trips or parties... Well, slowly he keeps defriending people right and left. When i say "defriending" i don't mean on Facebook. I mean, he literally will say "i don't like that you do this... which is why we can't be friends any more until you make it right". It's a harsh way of communicating, and I'm afraid he will just keep doing this to the people that are most important in his life. He comes to me to tell me about everything, and I'm not going to tell him what he should do or what he should say -- I just listen.
So this is my question for you: when you see someone having a hard time communicating in an adult way, and they keep coming to you to tell you about the details of various situations... when do you jump in to throw your opinion in? Or, do you not? I dont' like to ever give my opinion unless someone asks for it.
Re: De-friending
I'm not sure I understand - so he is a great, kind, loyal friend who also happens to be willing to ditch his good friends at the drop of a hat? What are these people doing that they need to "make right?"
I generally try not to offer my opinion when nobody's asked for it either. But here, I can imagine you might be starting to worry for your own friendship with him, and I think that could be an appropriate thing to bring up. Something along the lines of, "I've noticed you've lost touch with a lot of friends lately, and I'm concerned. How do I keep from doing something that is such an affront to you that you won't want to talk to me anymore?" may open his eyes a little.
It could also make him angry and de-friend you, who knows.

"You know you're in love when you don't want to fall asleep because reality is finally better than your dreams." - Dr. SeussThis - I still want to know what they're doing to piss him off.

"You know you're in love when you don't want to fall asleep because reality is finally better than your dreams." - Dr. SeussWhat is with people like this? I really don't get it. It's not fair to make friends walk on egg shells for fear of being "written off". At least this guy confronts the person to let them know they are being written off, but I don't know what ever happened to giving someone a chance to fix it or work it out.
People aren't perfect. They may make mistakes or piss off their friends. If someone is a good friend they'll at least communicate about it first before writing that person off as dead to them. lol. It's so dramatic!
If I were in your shoes, next time he tells you he is writing so-and-so off, try reminding him of the good things about that person, or defending them a bit. Maybe you can convince him to not be so brash in writing people off. Or this guy's future is gonna be pretty lonely.