It's definitely a complication, but others have gotten past it. If you've been as radically honest about your inappropriate relationship when talking with your MIL and those others you've exposed to, I think the complications can be managed.

Don't buy into his "justified revenge" theory though. The old saw about two wrongs not making a right clearly applies. Additionally, it could be said his was the worst betrayal because he knew first hand the depth of the emotional impact it would cause. Revenge isn't the best of motives in any human endeavor, btw. I don't like people who act out because they want to "get even."

Your MIL is a counselor, right? Maybe it's time to sit down with her some morning for a nice conversation over a cup of coffee? Or how about bringing it up with your IC?

BTW, any progress with finding WH an IC?