I'm sooo sorry to read this. I don't have too much time this moment but I plan to come back to your thread and be here for you (and hopefully come up with helpful wisdom...).
The one thing I will say. I don't believe it's wrong to stay in a marriage for children... When my children are grown I plan to reevaluate my life, marriage, etc... hopefully I'll want to stay. In fact, I saw a book just on this topic. I'll have to go find that and pick it up if it's still there....
One thing I will say, my husband has had more than one affair, tried to divorce me twice and MLC was a lot longer than I realized (but looking back I can see the signs). Your husband may still not be out of the MLC woods...
What about ADs for him? Has he tried those???
My guess is the feelings he gets from this affair are like alcohol or drugs to someone with an alcohol or drug problem.
Hang in there buddy. {{{{{hugs}}}}}}}
There is no arriving, ever. It is all a continual becoming.