That's what drug dealers do, they pretend to be your friend and give you a free sample just to get you hooked, then next thing you know you're sucking dicks to get your next fix.
I think the manga description might be wrong and this is a different guy every time, and each of them cheats and breaks up with a different gf every time.
Somewhere out there, there is some seventeen B-cup gfs crying about it all. Maybe they can form an advocacy group.
Maybe the bullies are much smarter than us commenters and they already know that the "bullying" attempts will only cause Takada and Nishimiura to get even closer, so they continue doing it as good wingmen?