Nobody said anything about whether she does or does not have the right to decide her own life. What I'm saying is how choices like that usually play out in real life.
Black-haired does want to have a normal amount of sex/ intimate physical contact but is ignoring her desires for the sake of the gf, see: how she awkwardly laughed when MC asked her if she liked sex, lowered down to kiss the blondie's neck but stopped short when the latter didn't like it, hesitated to give her even a peck on the cheek and had to stop afterwards to check if her gf's okay with that (blondie's surprised reaction implies this is not a common occurence). That and when confronted about the issue, she simply waved it aside and said sappy things like "everyone is different, just accept yourself and be happy". Yes, everyone is different, and that's what causes problems in relationships when one's needs is being unmet by the other because it is her dislike. She still hasn't solved the practical problem of how she'll satisfy her needs yet. The only thing we're shown is that she completely ignores/ pretending she doesn't have needs/ it's no big deal so as to not make her gf feel guilty. Apply this to any real life relationship and you'll see how it wouldn't work out in the long run, and even if it does, one party is gonna be extremely miserable for as long as it lasts.
This... martyr archetype who has no needs of her own and only exist to fulfill others' (usually the MC's) desires is ubiquitous in media for obvious reasons. But it usually manifests very differently in real life due to how human psyche works. I know the type. They aren't actually selfless. They still have needs and wants like everybody else, but for one reason or another tries to suppress it for someone else's sake, but those unmet desires of theirs aren't going anywhere, they're gonna cause resentment, lots of resentment, and when they can't hold it in anymore, they explode. Either onto the person who caused it or someone else. And then back to another martyr-ing cycle. That's how it works.
I see no character nuances here. Wanting to be loved by normal people but feeling insecure due to being unable to meet their needs is like, the crux of the asexuals' dilemma. The author tries to solve that by creating a cardboard character who still has sexual needs but happily casts them aside to please the MC. A more elegant solution to the problem would've been to hook asexuals up with each other.
