AceCase

YURI KATSUKI & VICTOR NIKIFOROV IN YURI!!! ON ICE (2016)

Neil being demisexual is literally perfect for Andrew. When they first meet, Neil "not swinging" gives Andrew assurance that Neil won't be sexually interested, which allows Andrew to feel safe enough to eventually become close to Neil. I think that Andrew's fear of being the object of sexual attention is partly why he exclusively spends time with people who won't develop sexual desire towards him (the monsters: his relatives + a straight dude; and Renee, from whom he extracts the reassurance that "I don't kiss heathens").

Then, once Andrew gets close to Neil and starts developing feelings for him, Andrew ALSO gets the reassurance that Neil actually does swing. For him, specifically. And Neil's swinging is nothing to do with the physical features of Andrew's body or with Andrew being available and willing. Instead, Neil values and loves the parts of him that Andrew himself has already offered Neil. This couldn't be more perfect for Andrew! Neil is a pipedream. A man for whom loving and respecting Andrew as a person is a precondition for even wanting to touch; a man who won't ever push Andrew to cross a boundary, because his own desires are completely enmeshed with his love for Andrew. Andrew has won the lottery of life.

And for Neil, too, his demisexuality is overwhelmingly a positive thing. It means that Neil doesn't have his head turned when it would have been dangerous for him. Instead he falls for a man who makes him feel safe and cared for. In fact, Neil himself acknowledges this when he first decides to kiss Andrew, reasoning that "the idea of Andrew was so intertwined with the idea of Neil's safety that this too was a means of self-preservation". Also, once Neil recognises what he feels for Andrew, he never has reason to doubt it. Neil doesn't get casual crushes, so he knows that what he feels is The Real Deal.