bugsy, what a time you're having. I think you are doing the right thing in asking your dh if he wants to leave to sort himself out. Does he realise that it's one thing having a family you can return to at any time, and quite another thing in leaving a family for good? As the song goes, freedom's just another word for nothing left to lose.
I wonder what he'd feel like if after hearing his tale of woe you'd said 'Ok, no problem - move out and don't come back. In fact I'm seeing someone else who'd really like to move in with us'
I hope whatever he decides is good for your state of mind. If he decides to go temporarily, I hope you can get the practicalities worked out on joint terms not just his terms. ie how and when he contacts you etc to keep some control over the situation.
I know you feel you've got to let him do his thing, and that's a really strong, brave thing to do, but do make sure you don't suffer, and make it clear you will be getting on with your life, not just waiting around for him. Anyway, that's my advice, fwiw.