Yes catperson, you do need honesty in a marriage, but it should be freely offered. Confrontation and snooping aren't going to accomplish anything other than pushing your partner further away.
I agree with this view; and agree with the first part of what Starsky wrote, about assuming that there is probably at least an EA going on, because all the symptoms point to that.
but I would not search for "solid proof" as Starsky and CP suggest. now is not the right time for that. I would just consider this as part of the general craziness of his MLC.
if you find "solid proof" and confront him about it, is that going to move you closer to your goals, or farther from your goals?
at this stage, searching for "proof" and/or confronting could actually take something that is *not* important and make him feel that it is more significant than it really is.
think of a 5-year old playing with a toy that you don't want him to be playing with. he actually might be starting to lose interest in it, and be about to put it down anyway, but if you say, "give it to me right now!" he will say, "no! I want it!" and hang onto it as if it were the most important thing in his life.
remember, this is not e.g. a coworker that he gradually developed an attachment to - that might be true competition and then you might want to confront. but this is all part of his MLC craziness, and it is better to ignore it along with the rest of the symptoms and just "ride out the storm".
if you are waiting for a hurricane to pass by, you don't start doing repairs while the hurricane is in full force. you wait till it has passed by, then you start working on repairs. in the meantime you do what you need to do to protect yourself and your family and get through the storm.