Story Cursory Review:
I'd be baffled by this, but okay: seeing as canonically at least, Regina was kind of tutoring Emma on magic/occultism; it would follow that strange desires would tend to result- ironically you're way closer to the effects thereof than the show's writers were: it messes up the people who go into it, big time!
Yet the idea of Henry's moms getting into that kind of relationship really is something that'll turn heads to say the least, not to mention when their neighbors see them kissing on a walk: lets just say the tabloids will then have quite the field-day to put it mildly, on them and at their expense!
Fun? Oh yeah, but truly messed up domestic lifestyle going on in regard to this, though I could perceive Regina having cast a bit of a spell on Emma in the backstory to this so she could use her- she did cross those lines in the past: with Graham to be exact; one of her more criminal acts!