Because dohu used to be a yaoi author or sum shi and he used to use his relationship with juheon as a material and when juheon found out he got really mad and left but they both liked each other so…..
Cause dohu couldn't get rid of a word document for a character he was basing off juheon and he found it before he could and since he's got trust issues he assumed that meant dohu was using him the whole time and dohu is emotionally stunted and also felt guilty because he was using him at the start... so he didn't really fight for him since he didn't feel deserving
(or try to explain his actions at all)
(⊙_◎) the uke is so protective of the seme, btw why did they break up. I forgorr