My fiance [22 FtM] came out as trans after 4.5 years together but I [24m] am straight

So after 4.5 together with my fiance he came out as transgender. This happened almost two months ago but I'm only now accepting the facts, the girl I love do not exist anymore and now there's a boy that I still love but don't know if I can give on my sexuality to stay with him.
Since I was in denial our relationship is in a bad situation because of this and I will have until Monday to decide if I want to break up or stay with him and accept him as he is. The thing is I don't want to break up because I do love him more than everything and even thinking about that makes me feel as if I would rip my soul apart, but I don't know if, in the long run, I will be able to have a romantic relationship with someone from a gender that I actually don't fell sexually attracted.
Some important information:
He is my first SO so it makes everything even harder to decide, since I can't really use previous experience and this makes me feel that I would be losing a important part of my sex life by staying with him.
We live together and our coexistence is great. He makes me a more organized person and I make him feel safer. We really like and care for each other.
He decided to forego HRT to stay with me which makes me feel bad because I don't want him to give up on what makes him happy but at the same time I'm sure that with HRT the relationship would be unbearable.
TL;DR; My fiance came out as transgender, I do love a lot him but don't know if can keep the relationship since I'm straight. And I have until monday to decide.
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Source.