Give Love, I wanted to write this as well, but couldn't put it in a "decent" way.
I know from past experience (RAH) sometimes when something is new and they find that someone else shares and shows "interest" in them, they tend to get a big head, and start thinking with the wrong part of their body. Maybe someone else is giving him some type of emotional (not saying it's right, because believe you me, it's NOT) bond that he thinks he needs.
I went through a similar situation when my RAH was still active. All of a sudden there were phone calls coming into his cell phone as normal phone calls, then when I answered them (due to him driving) she asked to speak to him, I gave him the phone they spoke and got disconnected, she called right back and blocked her number. Phone calls to and from her all the time, him stating that she was coming over to say hi and good mornng everyday while he was at work (she worked across the street & they went to the same bar). I told him that it was behavior that NO married man should be doing and I got the third degree.
I still say, you should consider attending some open meetings with him. They will be very helpful.
REMEMBER, if he chooses to go out and drink it is NOT your fault. The three C's are so important here.