Big hugs to you, friend. It sounds like things are moving quickly and I can completely understand your shell-shock and feelings of betrayal. My partner and I were married for six weeks when he came out to me as trans. I felt like those old cartoons, when Wile E. Coyote runs off a cliff, hovers in midair, and then plummets to the ground. The reactions were kneejerk and instant: I can't do this! I'm a lesbian, not straight! I didn't sign up for this! How could you have waited until after the wedding to drop a bomb like this? His "boy" name felt awful and weird in my mouth. Every time I had to say "he" I felt like throwing up. It was really rough for a long time.
Like you, I am comfortable in my sexuality. I slept with men for years and it never did anything for me. Finally I met my partner and, after a long coming-out struggle, ultimately realized and embraced my attraction to women. Now I'm back in a relationship with a man. Sometimes I'm OK with that and sometimes I'm not. He hasn't started transitioning yet (military), but he wears binders and men's clothing and cuts his hair as short as military regs will allow. I've adjusted to that, but I worry every day that when he starts testosterone I won't be attracted to him anymore. It's a shitty situation to be in, and there isn't much I can do but wait and see what happens.
My first suggestion to you: find a therapist for yourself. It was so helpful for me to have a safe space where I could say whatever I wanted to say about my partner -- whether it was kind or downright nasty -- and give vent to all the emotions I was feeling. My therapist let me panic, scream, cry, swear, and anything else I needed to do. She didn't tell me I was being silly when I cried for an hour about chest hair and penises. Second -- and this is the hard one -- take care of yourself. As partners we are expected to give support, but our partners are often too wrapped up in dysphoria, the excitement of coming out, and the process of transitioning to support us. Your world has just been rocked to its core. Have a beer, get a massage, eat a slice of pizza -- whatever you need to do to give yourself a moment of Zen throughout the day.
As /u/sevenyearsgone said, this is going to take time. You might be fine one day and sobbing the next -- and that's OK. Take care of yourself. This is new and scary, and we're here to talk you through it. The temptation for me was to wallow in panic and uncertainty, especially since my partner and I were in a long-distance relationship when he came out, but I know now that you have to keep moving forward. Even if it's just baby steps. Even if some days you slide backwards. Just keep moving. We're here for you!