
When we read a story or someone tells us a story we are getting fumed and saying things like "I am going to kick his butt!". In reality you deal with things (if you are a civilised intelligent being) like Keigo. Chi was hurt only because of his insecurities. He could stand up to the model and say "Look Mofo, he likes me and I like him, go f yourself". But if you think you are not good enough other people will try to move in between. Keigo, when he realized that the model moved past the "I am sister's good friend, ow I am so funny" to "I want to date you/I am messing with your partner" simply told him (politely) to take a hike and leave them alone.

It's not easy you know. Someone who've only known he was straight will always find these things difficult and this is his first relationship to boot and we could tell how frustrated Chihiro is. He is young and already facing problems like these. Good thing sister is very open minded.
And yeah Keigo's too polite.

I agree except I think everyone in this story is past the age when bullying should be a problem. When you're grown up enough to be able to walk away, bullying shouldn't be an issue. If someone breaks the law by stalking or consistently crossing the line of too much being a nuisance, that's called harrassment, not bullying.
One of the few stories I want to jump into my computer and beat the shit out of this model dude and well one or two hits might have hit Keigo.
Bur honestly if a story gets me involved like this, the author did something right.