I'm sorry that he isn't listening to you. If he is normally someone who is considerate of your feelings, it's likely that the possibility of you transitioning is unearthing some anxieties that he doesn't know how to handle.
For one, Henry could be very right in that he worries you two may not be attracted to each other. He might think you will start liking women, as many people confuse sexual orientation and gender identity. Or of course, there is the worry that he may not be able to be attracted to you as a guy. Obviously I am FTM, but I have to be honest, I wouldn't know what to do myself if I had a female partner who wanted to transition. I'm not trying to be discouraging, I'm just trying to illustrate some possible anxieties he has, and maybe you could address them somehow. Of course if my partner turned out to be FTM, I'd understand their desires, but in terms of how to relate to them romantically, it would be a struggle. It would affect so many things. As a straight man, I've never communicated with a man intimately - I'd have to shift to seeing my partner as male, and then shift how I communicate with those I perceive as male. It would change how I touch them - I've never lovingly caressed a man, which body parts would I touch? How would I touch them without it seeming like I am caressing a woman? Would I want someone handling me like a man would handle someone? When I am with a woman I adore her body, could I adore a male body? Because he deserves to be adored and desired as the man he is. How would I avoid making him uncomfortable? How would I handle being perceived as gay, when I have never noticed a man in my life? People would talk to me as if I know what it means to be gay, as if I notice other men, and I wouldn't know how to do that. I tried to do that for years as a girl and everyone knew I didn't really like guys. Even though I am FTM myself I honestly would have no idea how to handle that. It would probably mark the end of our romantic relationship, even though I'd still love and support that person...but if I decided to stay with him, I'd have to relearn EVERYTHING I've ever known to be true to myself, at least in terms of intimacy. Not saying it's not possible, but I personally don't know where I'd start and I'd have to communicate with him.
At the end of the day, it's going to come up one way or the other. It's kind of hard to put gender issues back in the box once they are out. I think you will, at some point, need to ask him to really tell you why he is shutting you out. That you are trying to talk to him, but you just don't know how to get through, and you want and need for him to be open with you so you can find out how to proceed. Especially when you have been together for so long.