Romantic love can't solve everything. It can't wipe out years of abuse.
It can't overcome drug addiction. A person who has suffered such
problems needs time and space to sort themselves out. Often, running
into a relationship will only compound the problems, even sabotage the
new relationship. Drowning people can drag other people down with them.
In books of this type, the trope "I saw someone across the room and knew
we should be together" stops being cute and becomes intensely selfish,
even skin-crawling. Sure, the object of the pursuit will cave--that's what vulnerable people do. Doesn't mean it's right.
In addition, as I point out in a review of a light novel, if a person falls in love with someone with serious dysfunctions, might the person be in love with the dysfunctions? Or in love with the role of rescuer? What happens when the lover improves?
His "patient," then boyfriend, is aware of Kurose's past. Consequently, one of the most touching scenes in the series is when Kurose confesses, "You are nothing like him."
The behavior tics may have brought them together--and may in fact still define HOW they communicate--but Kurose fell for Shirotani (and Shirotani fell for Kurose) for his specific personality. The foibles are part of the attraction/charm, not the only thing that matters.