I think its because before, he though he was hated by him and that he was always treated badly by him and the person he found comfort in was the same one. I think zhaomu might feel like he was toyed with
it's hurt so much (TT) thank god happy ending, so Taeil still alive ( maybe he's in coma) and his spirit wondering around that apartment, so that's why he met Yuzu.
i continue read because of Taeyang. lil bit confused but i need to finish it.