I've not written to you before but your sitch has drawn some interest from others on the board since so many of us have previously found ourselves exactly where you are now.
I know just how exhausting this is and how it takes it's toll. My ex did much the same as your's, the only difference was that he didn't have his OW waiting in the wings. It got to a point where the only thing I had left was the LRT. Even knowing that Michele had warned about of the consequences, I knew it was time. Limbo is a horrible place to be. Besides that, I had 1 son and 2 daughters and I worried about what did this say to them. Even they were starting to look at me disapprovingly. I didn't want my son to think that this was an ok way to treat a woman, and I certainly didn't want my girls to feel that they had to accept this kind of behavior from any man. You see sweetie, someone has to change the dance. If your husband is in a true MLC, this could take years and usually does. Knowing what I do now, you're husband has no reason to change or figure things out. He has a safety net on both ends.
My best advice is before you do anything, make sure that you are at peace with it. I prayed so hard and finally realized that this was not in God's plan and I'm ok with that. In fact, so many wonderful things have come out of the what I thought to be the worst thing that could ever happen.
Life will be good again no matter how this turns out.