
I am ashamed that I skipped reading this because of the cover (cause I thought it was gonna be smut galore with blackmail or something, y'know the usual tropes)
This is honestly a palate cleanser from some of the BLs I've read recently. It"s so healthy, they're so nice and understanding of each other and they still get the butterflies after 4 years of dating I'm HSNFNCNFK
Even though Nick is super annoyed with lil' bro, I think he has superiority complex. He's annoyed but pleased with lil' bro following him around.
Also the teacher is someone Nick wanted to keep but couldn't cause dada issues, and Theo's having the chance to be with the teacher pisses Nick off (I mean, it makes sense cause why does he keep interfering if he's over the teacher.)
Theo getting the teacher would mean two things: Theo getting over being a copycat of Nick and getting something Nick wanted, bruising Nick's ego even more.
In short, Nick is an entitled prick