I found out my partner wants to have intercourse with a femboy, and i feel insecure

Hi, I'm currently going through a mental block. My boyfriend recently told me that he would be willing to experiment with having sex with a femboy. In my mind, I was picturing a guy with a petite body who likes to dress in "womanly" clothing. He showed me videos of what he likes and its the opposite of what I had in mind. He likes a guy to have a feminine appearance and a feminine body but with a penis. Being as honest as I can be, I have never been into women. I can admire them and say that they are sexy and beautiful, but I have never found myself sexually attracted to them. I let him know that I am not opposed to the idea of ​​him having sex with a man but that I am not comfortable with the idea of ​​him having sex with one who looks like a woman...Now he is upset and disappointed that I don't like the idea. To be completely honest with myself, the idea does not sit right with me. it makes me insecure given that I don't have and will never have a penis, and he finds himself attracted to this. As I was talking to him I vividly got upset but I tried my best to be as understanding and open-minded as I possibly could, and apparently, i failed. I told him that if he wanted that, that I could break up with him so he would feel free to do what he liked. he got upset at me for even suggesting that and told me he only wanted to do it if I was there, that otherwise, he will just block this idea of his mind. And that just made me feel 1000000% worse because all I wanted was for him to be happy. I don't know how to handle this situation, I am so embarrassed with myself for not being okay and feeling so insecure over this.