Hi PB,
I am bipolar I, although I rarely have a manic episode, mostly hypomanic or depressed. I agree that you should definately do some research on bipolar in order to help you determine what is a result of your husband's diagnosis, what is his meth addiction and what is related to other problems. I think the main concern is that even if this behavior is part of his illness, is this something you are willing and able to be a part of? His bringing someone else into your relationship is obviously hurting you, no matter what is causing this behavior on his part. If you are both willing to work on this together, I think you should really start with marriage counseling together as well as participating in counseling for his other problems. Trust is an important part of a relationship and if you feel he might be pulling a fast one on you, you owe it to yourself to make sure you're in a situation where you can trust the person you are with.