I don't know if I have any advice per se, but I wanted to say you are definitely not alone. I've struggled with this at various points throughout my relationship (I'm straight cis woman, he's straight ftm, and I guess we're a bit both queer).
Don't be too hard on yourself. You are only desiring to have sex with your boyfriend in a way that feels good for you. It's hard when you experience him as the man he is, but the parts don't always match up. That's not to say, the parts are required to be a man, but If you've been with cis men before it can feel at times something's missing. I feel guilty about that at times. I call it dysphoria by proxy. I'm not sure if it's mine or me picking up on my BFs feelings.
When we first got together, one of my biggest fears was he was going to want to be penetrated because I was not into that... At all... He's not. And if he was, I couldn't do it. I don't even like to penetrate myself.
When we have sex, I think about his parts as male and try to focus just on making him feel good. I never want him to feel less of a man, but now that he has decided to have a phalloplasty I am excited. I crave that intimacy with him. If your BF is having bottom surgery, then you can take comfort in knowing this is temporary. I don't think there's any "getting over it." You like what you like. Has he made a decision of which type to have? Depending on what he chooses, this might be something that goes away after surgery. You've obviously got a lot of love for each other, this is just one of those things we have to navigate. It can feel extra hard because your friends probably don't and you don't wanna sound like a hater.
Sent from my iPhone using Tapatalk