This is one of those stories people would view differently if the genders were swapped. Though there are many of those stories (not this exact setup, but close enough) as well, so it'd probably still work. Main difference is probably that people would be more accepting to the character rejecting the constant unwanted advances, which would absolutely be red flags IRL (but frequently accepted in cute romcom mangas).
Oh ya he messed up & more than likely went a bit overboard on putting his foot down in refusing her advances.
From what his character is and where the story is going, sure. But for refusing someone who's consistently refused to acknowledge being refused, not really. She's not entitled to him accepting her, but she acts like it. Unpopular opinion, but I don't think he's done anything wrong that matters.
But also from a story perspective, it needed to happen. It needs to get worse before it gets better, since it's not a slow-burn SOL.
Since it's a romcom with more emphasis on the comedy, it's fine if characters aren't what we would accept IRL, though. Makes for funny situations.