my (cisF) husband (FTM) just came out as nonbinary and I am not handling it well

My husband was out as a man well before I knew him, he started hormones before graduating high school. He has been intermittently on and off hormones (mostly off) due to fear of needles and lately, almost ambivalence at further masculinization. Even before today's revelation this started to stress me a bit because I know he has complete control over his body and should do as he likes, but he looked like an 18 year old at 20 when we met, and he still looks the same at almost 30. Someone on our honeymoon thought he was my son, we've had people not believe his ID, grandmas at the park think he is a teen dad. I don't want to be 40 and look like a creep.

We got married a few years ago, just had our first baby via IVF 6 months ago & a I had a very rough delivery/postpartum.

We were out on a rare date night and he said he's been thinking that when complaining about men, he doesn't always feel like 'one of the guys'/encompassed by that term, more in the group that would complain about men. That & wanting more gender neutral clothes, and he feels closer to 'masc nonbinary'. He said he doesn't want to 'detransition', doesn't want to change his name or pronouns but I don't know how true that is. I initially reacted positive/neutral but started spiraling and after he saw my reaction wasn't totally positive he shut down too.

I am bi and don't have a particular type, but I am pretty sure I will not be attracted to him if he steps away from masculinity significantly in dress, pronouns, etc. There's some feelings of betrayal, like: when I am still dealing with the effects on my body from pregnancy & our 6 month old needs so much energy and attention, how is this the best time to bring this up? Why now, in an almost decade of dating/marriage?

I also hate that I'm reacting this way, I love him so much, he is my soulmate and theoretically I shouldn't care what his gender is. But I do, I like that he's a man - he worked so hard and faced so much to be one! - and it terrifies me that this might break us apart. I pictured dying next to him, both of our parents have been married 25+ years. I have no idea how to handle this, other than booking couple's counseling which I'm doing immediately.

Sorry for the long post, if anyone has thoughts or advice please share.