Adrian, sorry I am late to post a reply, but I hope things are working out. I was in a similar situation as your husband is, and just wanted to give some hope that things can be ok if you do decide to transition.
My husband didn't come out to me until long after he had already decided to transition, and after already several sessions with his therapist. When I first met "her", I was attracted to the tomboy appearance, and assertive personality which he had at the time. Over time, going from dating to marriage, his tomboy appearence became more masculine, from his clothing to mannerizims, to haircut. I was still just as attracted, but had no clue what he was going through.
A couple summers ago we were out in public and "she", (how I though of her then)was mistaken for a guy several times. I made a comment to her about it, and that's what lead to her coming out to me.
His mind was already made up about it, so I guess that is where our situationis different. It was made clear to me that I would have to accept it, or at least try.
I was very shocked, but also took the time to research, and eventually went to a therapist. Yes, I admit I didn't want to lose the woman I loved, but realized it was my choice to stay.
I am glad I did! He is still the same person in many ways, we enjoy all of the same things we did before, some new ones too.
I am glad he made his decision on his own, because really it was his choice alone. I hope you do what you feel is right for yourself first and foremost. I think life is too short not to be the person you are. With luck, and lots of communication, I hope your husband can be as open as I was. It's not easy though! Feel free to message me anytime, or your husband as well. My husband has been on T for 1 year and 2 months now, and there are so many things that happen I can advise on. Best wishes to you both