>>57369017As an OG Advanceshipper, who remained such until XY, when I became an Amourshipper, my headcanon is that May eventually, and nonchalantly, springs it on Serena that she's had a relationship with Ash, one that she has assumed has remained intact since AG/DP, and it's made clear that May has always been completely oblivious to any hint of romance from Serena when hearing her recount stories about Ash from Kalos. Serena feels completely betrayed (again, May doesn't pick up on it) and by the time Serena finally spits her guts out to May, May agrees that Serena can have him, so long as Serena lets her keep a "friends with benefits" deal going with Ash on the side, plus the occasional throuple relationship. Lisia, overhearing all of this, tries to get in on it, but they both tell her to fuck off.