compersion & limerence

Yes, this was exactly my issue with the ending as well, although it sounds like I had it to an even greater extent than you did... I mean it's a clever plot twist but I just don't think there's any way for it to make sense, on a characterization level. If Selina actually buys her own schtick, then how does she justify to herself all the active deception she perpetrated on Margaret, AND ALSO all of the facts that she OBVIOUSLY KNOWS about Ruth, & how they make the con work? I feel like I can buy living with a high level of cognitive dissonance, but that exceeds even my ability to believe. Unless Selina is writing for the benefit of someone else, off-screen, whom we never meet... which is equally unsatisfying as there's no way to extrapolate the existence of such a person except by extending Sarah Waters an incredible amount of readerly credit that I don't feel she really earns here. I actually wrote a whole Affinity fanfic trying to find a way around this problem that I could believe, but I failed to convince myself. Those two Selinas are just too incompatible.