He DOES NOT LIKE IT when I don't talk to him. He tells me that he needs me to talk to him. He is going through a really tramatic family situation right now with his mom. He found out that his mom had A on his dad...and the lies that have manifested in the family are just now coming to a head. He says that he needs me right now for this situation, because I know everything and can help.
I don't think this is healthy for you, to continue to communicate with him at this deeper, intimate level. If it were me, I would tell him that "I'm sorry, we will always be friendly with each other, but you are leaning on me emotionally in the way that a committed husband leans upon his wife, and you chose to not have that kind of relationship with me anymore. Take these up with your affair girlfriend. I'm not trying to be rude here, I'm really not, but these kinds of conversations just don't work for me anymore."
I like the "this isn't working for me" construction -- you can use it a lot.
Your husband has made a choice, TAMF -- a very destructive choice. By continuing to be his confidante, you are enabling his bad behavior, in my opinion.
