My head and my heart are split; help

My (35 cis F) spouse (36 MTF, but still using he/him pronouns for now) came out to me about 6 weeks ago, and I’m still struggling a lot more than I expected. When we first had the conversation I think I went into something like “work mode” (I work in mental health). I listened, validated, asked questions, reassured, but realized later that I wasn’t having my own authentic reaction in that moment. I’m in therapy and so is my spouse now, but my therapist is out of town for 3 weeks and it’s truly rough timing for me. I’m realizing how much my head and heart are divided, and it’s destroying me. The logical part of me wants to be a supportive and affirming partner, and I of course want my spouse to be happy and become their true self. But my heart is not getting on board and I can’t figure out why or what the hell is wrong with me. My heart doesn’t want them to change. I love them exactly as they are, and them coming out was 100% a surprise. Aside from some more “traditionally feminine” hobbies, it NEVER crossed my mind that they might be trans. I’m scared of the rapid changes that are starting to happen, scared of the ones to come, scared of losing attraction (I’m heterosexual and really not sure if that is flexible), and feeling like I don’t know how to be a good wife anymore. Our marriage used to be the best, most stable thing in my life. Now I feel like I’m on a roller coaster I didn’t want to get on, trying to be supportive but struggling, and not knowing what to do. Should I fake enthusiasm? I’m finding myself clamming up because I know my distress is causing them more pain and discomfort than they are already dealing with. I feel like they deserve a better partner than me, someone that can be fully thrilled with their transition vs the train wreck that I feel like. Any support or advice welcome.