This Demon... really making it harder for our boi here.
the only real way outta this is to get Rikka's consent in all this. and still make sure she knows that she is his number 1. or at the very least confront her about this. the earlier the better. especially seeing as theres probably going to be another one getting cursed.
I think this manga is just unfairly rated because "oooh ntr...oooh cheating bad" but it doesnt mean having that happen means its a bad story. people forget its a damn story, not an educational book.