@bolognya Think it was mainly because of this chapter, the panels seem to be out of order.
Wen the guy meets whit the bully, its wen he says "Hi", after that he says the whole speach and thats wen the bully starts blushing.
But basically, the bully subconsciously liked MC but because characters gotta be dumb (as cliche demands), he went full 0 brain cells and started bullying him instead of thinking about the confession (probably in the subconscious idea of "if I keep blackmailing you there will always be a connection between us"), so, wen MC just decided to put a end to it and trowed at his face that he didn't feel ashamed that he had liked him, the bully finally to realizes that he didn't like the fact that the MC kept denying his love for him (basically giving the hint that the bully himself couldn't even figure out why he kept a connection trough all the years whit someone he supposedly finds discussing).
So yea, TL

R Bully kept bullying MC misunderstanding his own feelings as discuss wen he actually subconsciously liked the fact that the MC liked him so he kept a connection whit MC via blackmail, just to end up pissed at the end because MC ended things while realizing he wanted the MC to keep liking him.
Hope this helps.