Two guesses, potentially both needs to happen:
1. Dohu will commit some sort of self-sacrificing act or other display of loyalty/love. This is important bc Juheon does have some valid trust issues. Not just stemming from his family, but also the fact that Dohu himself has covered up his intentions and knowingly expressed misleading statements of affection. Essentially, he'll need to win over Juheon's trust.
2. Whatever evidence/blackmail that the aunt has against them needs to be cleared away. Recall that the aunt threatens Juheon around the time they break up, and it looks like its something that Juheon is still working on.
Love that idea.
What is your theory of them getting back together ????