Maybe because it's been years since they last met so the uke might've thought the kiss the same gave him when they were in highschool must've been a mistake so he tried to hide his feelings ever since
He still couldn’t resist his feeling towards him so he’s trying to make the best out of the any relationship that he can get from Yeon which was dunbar-hoobae.
wait...so if he is trying to avoid him, then why did he approach him on ep 1 (like on the day at the university where they met again?)