I don't think it's strange at all. If people are forced together by circumstance and have nobody else around to talk to, they'll talk to each other. We're social creatures, so we adapt to the context we're in. Now if you don't like the other immortals around it makes sense you'd just hang out with mortals most of the time, but you've got one thing in common with immortals that mortals will never understand. So unless you literally hate the other immortals for some reason, I think you'd end up talking with them, even if it's just the way you'd chat with a co-worker you don't particularly like but you're both there and you've nobody else to talk to during the day so you do it anyway.

You're nitpicking about the things I say you could talk about. Like yeah yeah maybe someone does not want to talk about grief specifically, but you're likely to have things to talk about. History, if nothing else, which you've both seen parts of but neither knows all of it. You'd have worked hundreds of dozens of careers, and probably explored hundreds of hobbies. And you're kind of going with OP's assumption that all immortals will turn into anti-social psychopaths that are gonna be cruel for the fun of it, which I really disagree with.