RaD's feed

Is it really normal in japanese culture to confess feelings to someone who’s in a relationship and attempt to pursue them? I swear in almost every romance manga I’ve read, it’s normal for side characters to actively try and separate the mcs and steal them but for some reason no one else in the story cares….the mc’s don’t even do anything either and just accept it as a challenge. I really this manga doesn’t do it. It should be more frowned upon and not seen as an everyday thing