I suspect I am mashing up ACD/'09 movieverse/Mary Russell/Irene Adler/Sherlock canon together, but I see Watson when he first met Holmes as very depressed and self-destructive. Honestly, why else would he attach so strongly to Holmes, so quickly? If Watson was stable and reasonable at the time, I suspect he would have tried to find alternate lodgings very fast. (Which makes Holmes a kind of horrible rebound relationship, but who are we kidding, Holmes/Watson was never known for being healthy.)

... and since I usually see Holmes as asexual, I feel like I have to ask: the extension to include asexual people is just the logical one, yes? While it seems canon that red romance seems to involve sex, but in my opinion, there's a difference between a non-sexual relationship with a moirail and a non-sexual relationship with a matespirit. And it is definitely possible to have FoeYay without sex, so that seems doable. A asexual sedoretu would seem to require replacing two or more standard sexual relationships with romantic asexual relationships, but that seems doable -- as I said, there's a difference between not-having-sex with a romantic partner and not-having-sex with your best friend. I suspect the problem would come with trying to figure out troll romance or a sedoretu for aromantic asexuals.