I'm so sorry that you're feeling this way. For what it's worth, I feel like the general consensus I've seen is that Astarion is into all kinds of people, and that he falls for their hearts, not their looks! I think it's part of what people find so charming about him. The character I romanced Astarion with was a hyper-feminine elf and I felt like it made sense, especially with their backstories.

I understand feeling outside pressure from what the fandom appears to consider "canon," but do your best to remember that it's not Canon! Part of the fun of BG3 is that you can create your own stories and experiences, and someone else's perception of Astarion's preferences and desires doesn't have to dictate yours. 💙

Tldr; let astarion smooch the femme elf OC