Jak, Although you are in a much better place than me, I can see many similarities.
My H never tried to confide in me that he was unhappy. Instead he chose to confide in OW/secretary. Unfortunately lots of us knows what happens when they start to confide in others. My H t will not go to counseling either. I know what you mean about sweeping everything under the rug. It feels like I'm on one of those wheels that the hamster keeps running on.
From what I have read your H displays the classic MLC symptoms. He is unhappy with his life. He doesn't feel like he has succeeded in his career. I'm sure the grandchildren remind him that he is not getting any older.
A MLC book I read was by Sally Conway called "Surviving Your Husband's MLC" I got it off Amazon.com. She goes right along with DBing, but explains MLC a lot more thoroughly. Her husband wrote a book for men on MLC. I think it would be good for your H to read. Your H admits that he is having a MLC, more than H admits. If you can't get him to counseling, I think the books would help.
Life's challenges are not supposed to paralyze you, they're supposed to help you discover who you are. -- Bernice Johnson Reagon