As for this particularly troublesome friend, I don't see much alternative to you saying, "I get that you're hurting about this, and that things are difficult and weird for you, especially concerning these other friends. But I can't help you with this. I can't listen to you discuss it. I just don't have the emotional or physical resources to be involved in your dealings with them. I wish I did, because I know how much you care. But I cannot help you. Please, you need to discuss this with someone who is not me."

I'm going to give a big yes to this. It's both your right and your responsibility to yourself to say "I'm sorry, I just don't have the emotional resources to deal with this right now."