@Evelyn I did this evening
Hopefully, you guys can help in some way... it sounds like his friend is in an abusive relationship :/ he might not be willing to leave her, but if anything, it might be nice to have someone to talk to about what's been going on if he's willing to open up. That's probably how I would initiate a conversation with him, whether that be by you or your husband... maybe mention what you witnessed the other night when she became confrontational and ask how you can be of best support to him. I'm not sure if bringing up the information she revealed to you is the best option or not. If I were him, I'd want someone to tell me... but you/your husband might have a better idea of what to/not to mention.
Not too late to say something. Especially if they are in your house. You get to see your own rules
Personally, I would mind my own business. I was in this situation before and I wasn’t believed…I lost the connection and was made into the villain in the situation. I think it would be difficult for A not to know on his own and it might be more challenging for him knowing others know, like it might uncomfortable coming around knowing that you know that info about their relationship. Better to affirm, without specifics, that ya’ll care about him and would be there for him if he needs it.
If I were in your position, I would confide in my husband first and foremost.