SPOILER.......
From what I had heard. MC's mom paid ML to be his tutor and also acts like a survailance/ keep an eye to MC before, and I think now, it is the same, paying ML to keep eye on MC... this also occurs to MCs friend while MC is in US. So basically MC's mok paid both ML and MC friend to have a connection with MC. ML is not paid to date though.
The hidden deal has some secrets with ML identity thus before, MC's mom has a hold on ML
dude.....the only time he has done that is when he was tutoring wooyeon. the reasoning why dohyun did that is cause dohyun was abandoned by his real parents then, wooyeon's mother started sponsoring dohyun and dohyun also got adopted. he only did that cause she was sponsoring him back now. he stopped doing anything for her once he went to the army, he approached wooyeon cause he wanted to for himself, not for anyone else. he did everything he could so wooyeon could enjoy his university life knowing how sucky and how strict wooyeon's mother is. wooyeon did misunderstand him at first when he found out that dohyun worked for his mother, think he was still working for her. they communicated well, solved the misunderstanding and are happily together.

Oh dohyun, it breaks my heart to know what you'll do to my baby, but you are so freaking handsome I feel like I can forgive you for now.