I am sorry you have found yourself in this situation, and back here, but it is a good place when faced with a D. I guess more info would help us to see where one can help. Sorry to suggest this, but is there no a OW? Men don't generally leave with such determination unless there is someone waiting for them, or at least, not as far as I have experienced on this site. Many have said 'no', only to find out differently. If that is the case, then at least you know what you are fighting.
If there is definitely no OW, then I guess the best thing is to give him his space. Actually, that would apply even if there is a OW. The list is pretty good, but impossible to take in all at once, so take small steps, one day at a time.
Anyway, it's late, but I just wanted you to have a response, and a welcome to the board.
I wouldn't just say "Men don't generally leave with such determination", I would say men or women don't generally leave with such determination unless there is someone else waiting.
The observation is sound, oncemore this is definitely something to look for but you don't give any impression that your husband is having an affair. Your husband just sounds like somebody who is fed up with lackluster effort and someone who is willing to quit and offer divorce as the solution to the problem. I doubt you only mentioned "divorce" once to him, he probably heard this several times from you.