So in short, fuckboi is omoshiroi (how interesting) on this MH because she isn't fan girling on him like every walking female on the vicinity that hops on his dick at sight and that she is into other guy upsets him so he goes lengths to get into her panties with the good old "practice for your BF" (and gets triggered when she in fact does it with her BF without falling for him).
It's an interesting NETORI story where the MC is a scumbag.