Ah. Oh dear. That sounds a bit odd. I mean, why wouldn’t she just talk to him herself? Asking a friend to intervene with your husband like that is a very strange thing to do. Especially if your husband is a lovely person who she knows is a bit worried about her.
If that’s actually what happened, my money is bang on affair and she’s using you to soothe him because she knows your own situation would make you sympathetic to her.
Because, no offence OP, if she genuinely wanted to get through this situation with him, I really can’t see why she would ask for support from someone who’d sacked off her friend in the same situation. If she’s not having an affair, she certainly seems to be using you to help engineer an out for her marriage.
I think it’s really unfair on both you and him to have got you involved TBH.