Should I go over to comfort my friend or let him be with his friends?

I think that if you know your friend's other friend at all, then you could always go over for the sake of comforting all three of them. After all, even if they do want to reminisce, I'm sure you won't be the only visitor. Yeah, I think you should ask first, maybe. Don't come on too strong to them; be cautious. But basically, try to do it for all three of them, if that's possible.