Uh, this is just a guess but I think the demon king approached Ye Li because he was Zhu's reincarnation, and then as he got to know the actual person he became more attracted to him? Idk that's just what I think
That was the reason before but then he found out that Ye Li wasn't zhu reincarnation and actually did fall in love w him.
He found out that he wasn't reincarnation so he wanted to give up but then as u can see the uke looks like he's already in love with him in the raws he gains his memories back of the spring god and they will become lovers I just read the latest chapter and they were getting married when the uke's father attacked them in the middle of the wedding
is the demon king in love with zhu's reincarnation, only because of zhu or like is he in love with the ACTUAL person