I don't think this though was meant to be taken as serious. It's just there to highlight Aya's overall anxiety and her worrying about everything. I think this will stop there, and there won't be other mention about cheating.

Hopefully and probably. But it is weird to use that same thing again in such a short time for it to just be a throwaway gag. Especially when we haven't had much time with them yet since the timeskip.

If people in works of fiction talked like sane people, half the books, movies, TV shows, and gay-ass manga in the world wouldn't exist.

And we would all be better for it. These kinds of contrived "conflicts" always feels like low quality fanfiction where the author either don't know how to create compelling communicating characters or they are out of ideas.