Feeling bad for Satsuki, since it's not like he can help his attraction. It's possible he's in some way not straight, though. I mean, for a while I was attracted to this fairly feminine gay boy back in my youth (ew, feeling old rn) and I liked feminine guys a lot more than I do now, and the biggest reason for that is because I turned out to be bisexual and I was redirecting my attraction for women onto feminine guys.
Based on his reasons for liking Rika, his gender might not even be as much of a factor as Satsuki presumes. He seems to like Rika for who he is but, y'know, comphet is a thing. So Satsuki probably presumes he, as a "straight" man, must be attracted to Rika because he's afab; even though there are other possibilities that would allow for Satsuki to be attracted to Rika without presuming that he must be viewing Rika as a "girl" on some level.
Like...bruh, you could just be not-straight. Rika's trans manliness could be part of the reason you find him attractive. Consider. Please.