Ok - I was one who had A. I lied for years about extent.
It was not until he stopped being available and stopped including me that I came out of the fog.
I had no contact with OM but I shared a secret. I no longer share the secret.
I am fighting tooth and nail to save my M.
There has to be something in this not being available to spouses, not saving them, not loving them. I think it is human nature to want something you cant have. Our problem is though, making sure that is not the only reason the M starts again.