Kyunghoon and Heechul dated for the two years they filmed Knowing Brothers. It was until it felt too much that their relationship went downhill. When Heechul begins to date someone else to start over, he doesn't realize that Kyunghoon still loves him.

"Ahn Sohee vs Min Kyunghoon?"   Heechul knew that he would eventually receive that question from his boyfriend who got jealous the entire episode.    

Heechul thinks he is a bit special because he is the only one Kyunghoon talks to. 

Heechul is a busy guy. He works a lot (especially promoting with Super Junior and variety shows) and now he has to deal with his 33 years old boyfriend who constantly needs attention.

[cross-posted on ao3] Heechul can only be these things for him

Kyunghoon is always told that he is one of the rare celebrities that have the same personality on screen as well as off screen. The only difference for him is that he is always more brave to show skinship with Heechul on television, but off screen it wasn't possible because of his wavering feelings for the other.   He really is a coward.

It's not easy letting go of your impossible dream a second time.