I'm always a sucker for the in-denial-to realization to lovers trope.
Jaekyung has 100% caught feelings for Kim Dan and the dude is much more in denial than the latter. He's also extremely possessive of him as well. Remember, he's an absolutely discipline and focused guy. However, Kim Dan was just having an innocent chat with YoonGu and that had him breaking away from his workout and snatching Kim Dan so fast away from the poor lil clueless fellow.
He also wouldn't let Kim Dan go on the out of town match with the other guys. Lowkey claimed him by stating Kim Dan lives and cooks for him as well. XD Paid almost all his debts so that Kim Dan really can't leave him too. Also made him live with him when he could've left him to fend for himself, thrown him to a team mate or easily help him with another place to live. The debt arrangement is really just a pitiful excuse at this point.
The new guy is obviously going to be much more of a threat, and it's going to so much fun to see a more upfront green-eyed Jaekyung. Ha!