"LFL - I know he's not happy...I know he's got to be holding something back. How do I crack the code?"
Well, you can't MAKE him open up but looking back I would have really pressed my H on the resentment issues, particularly me not working once the kids were born.
I think he always resented being the main financial support but would never admit it. That's the problem. They still may not "fess up" because of guilt or whatever. He thought the kids needed Mommy at home but it conflicted with him wanting me to put my master's degree to work. Took it out on us in the bedroom (and not in a good way, lol!)