I agree with what you say. Love does not equal sex, and the clear separation between the physical realms and the mental realms. That said, I do think that sometimes when there is a strong mental bond, the physical form instinctively yearns to match it. Falling in love with a brain is one thing, but I think a desire to become one on every level and aspect of the human experience will follow. There are times when sex is just sex, and there are times it's to serve a greater purpose of becoming as closest and intimate as possible to the other, which I think might be the case in Demian. I don't necessarily think Sinclair a gay character or anything. We're all on the spectrum of sexuality. I think he is in love with Demian on many different levels, and it felt natural for them to also show their love on the physical level. Attraction, when strong enough and runs deep enough, is equal across all realms. Like you said, love doesn't equal sex. But sex can be a manifestation of love.
I don't necessarily think Sinclair a gay character or anything. We're all on the spectrum of sexuality. I think he is in love with Demian on many different levels, and it felt natural for them to also show their love on the physical level. Attraction, when strong enough and runs deep enough, is equal across all realms. Like you said, love doesn't equal sex. But sex can be a manifestation of love.