So in '05 you indicate you came out as gay. Yet it is not important to you and are willing to close the M and be exclusive with your H.
Don't get me wrong here and I'm saying this as tongue in cheek, but I'm thinking that at 22, your (now) H was probably a fairly typical male who was probably turned on by the idea of your interest in women. I certainly would have been... Not to mention the opportunity for him to play the field. I'm betting he figured he had it made and possibly liked to brag about that to his buddies... at the time...
That said, the harsh reality probably caught up to him and now the excitement has finally worn off. I'm sure it didn't just "happen". I'd put bets it has been building up for quite a while. Possibly when you became open about being gay. That doesn't really matter except to point out that your H is not likely MLC, rather certainly a WAS. Your effort here and now will be important factors as to whether your M can be saved, or not.
I think it's really important right now though, for you to pay attention to what your H's complaints are. Giving him space will allow him to work through his own issues, but right now... it sounds like his biggest concern might be that he doesn't trust you.
That might sound a bit hypocritical, considering he chose to be in an open M. But it appears that he wants to be with a heterosexual, monogamous R now. And he's probably hesitant to believe that you could provide that for him, even though you SAY you can. ie. It's a lack of trust.
So, certainly no one can predict the future. But do you feel that you could live the rest of your life in a hetero, monogomous M? Not just "live" in that life but embrace and engage that lifestyle, completely?
Not to mention the opportunity for him to play the field. I'm betting he figured he had it made and possibly liked to brag about that to his buddies... at the time...