SPOILER...
in the novel. Jaeha's inner dialogue kinda explains why he wanted to divorce ML. Not because he hates him but he loves him so much that he thinks, that now he cannot give something to him which in MCs mind makes him useless to his bae. So divorce is the only thing he can offer to free him/show his devotion. Kinda like saying: loving you so much that I am willing to let you go kind of feeling
He is bad at reading MLs actions so he just assumed ML tolerated him or he does his part well enough, not knowing ML also loves him dearly thus him tearing the divorce papers.

Im super confused about the divorce thing??? The talk didn't make any sense and everything until now shows that they lack communication but they clearly care about each other???