My Husband came out as Gender Non-Conforming

I have considered myself an ally for my whole life. My husband of five years, and whom I have two kids with, a two-year-old and a 2-month-old, has just told me he (I asked him on his pronouns and he wants them to remain he/him for now) told me he is gender non-conforming. We had a long conversation about what that meant for him. I told him I am not angry for not telling me, I am angrier at the society who made him feel like he couldn't tell me. Since then I can't believe how much I have been struggling with this. All I want is to be supportive. I have read books and documentaries on exactly this. I thought I would handle this a lot better than I am. I can't help thinking selfishly. This change has been overwhelming for me and I am trying to be honest with him however he told me I am more important to him than his identity and it makes me feel like if I say anything negative he won't feel like he can be his true self. I do not want that. I want him to be who he is. So I am turning to you guys. I would like a place to discuss my feelings first. I want to be supportive of his transition without making him feel uncomfortable in an already uncomfortable journey.