I have a feeling that people can't understand what's going on inside Jun's head. He's just very self-aware and tries to control his feelings. First, he knows he still has feelings for Yohan, which makes it difficult for him to "move on." So, he tries to convince himself to like Jaehyeon because he knows he'd be the better choice. Second, he doesn't think that Jaehyeon likes him in "that way", nor does he want him to. Jun is trying to develop a one-sided crush so that he won't be controlled by his feelings for Yohan anymore. He doesn't plan to let either of them know about any of this or make it obvious. His whole thought process revolves around his own feelings and how he tries to handle them. He just wants to graduate and not keep in touch with anyone from high school after that. To do so, he plans to maintain a good but superficial relationship with Yohan while replacing his feelings for Yohan with "created" feelings for Jaehyeon, which can be easily cut off when it's time. Jaehyeon is unaware of any of this and is only nice to him without seeing him as anyone special, therefore he won't get hurt in any way. He doesn't plan to hurt anyone and just thinks about what's best for himself, so why is everyone hating on him?
I have a feeling that people can't understand what's going on inside Jun's head. He's just very self-aware and tries to control his feelings. First, he knows he still has feelings for Yohan, which makes it difficult for him to "move on." So, he tries to convince himself to like Jaehyeon because he knows he'd be the better choice. Second, he doesn't think that Jaehyeon likes him in "that way", nor does he want him to. Jun is trying to develop a one-sided crush so that he won't be controlled by his feelings for Yohan anymore. He doesn't plan to let either of them know about any of this or make it obvious. His whole thought process revolves around his own feelings and how he tries to handle them. He just wants to graduate and not keep in touch with anyone from high school after that. To do so, he plans to maintain a good but superficial relationship with Yohan while replacing his feelings for Yohan with "created" feelings for Jaehyeon, which can be easily cut off when it's time. Jaehyeon is unaware of any of this and is only nice to him without seeing him as anyone special, therefore he won't get hurt in any way. He doesn't plan to hurt anyone and just thinks about what's best for himself, so why is everyone hating on him?