firm communication about your boundaries and acceptance that it's gonna get hella more uncomfortable before it gets better.

i found an approach that works, especially if the conversations or vibes might entail a lot of venting or wasteful negative exchanges is asking them before they run-off:

Are you looking for comfort or solutions?: as in (your boundary), i don't have the emotional energy to hear your bitching kinda thing lol, but if you want to have a healthy conservation, we can work on solutions together.