Even if it wasn't cheating, she was still using her position to manipulate the pageant manager without letting her boyfriend know. That type of manipulation should be AVOIDED.
Right? Either manga will take place WHILE they're dating or BEFORE. And, even if the manga does show them dating, it doesn't last long after they are a couple.
Welp, this is the past, we already know how this'll turn out for the other dude. Absolutely terrible. This'll probably be used to show how they built their bond or smth.