My H did the same with me - started moaning to me that OW wasn't treating him very well. She was distant sometimes and not very nice to him.
It really really bothered me that we were having that convo and it was partly what made me decide to start LRT. Next time he and I spoke, I told him I wasn't willing to be his friend and talk to him about his R with OW. I was his W, and his R with her had been a betrayal of me - not what 'friends' do.
He apologised and said he'd probably said too much. I've never asked him about OW since.
