Unfortunately - I'm not sure. It took me two or three months to figure it out in that case, and while I remember the revelation that "This is a healthy relationship", I don't remember anything in particular sparking it.

If this relationship ends, I still don't know what criteria I'd use to identify what I'm looking for. (She messaged me on OkC, actually; perhaps the only woman to do so who wasn't threatening me or who hadn't read my profile at all, although I fixed the latter by making my profile picture deliberately off-putting to the sort of person who wouldn't read a profile in the first place.)