Responses
Sooyoung is a man with pride. He rejected taesung few times. Taesung took him to his mansion before but sooyoung fight and rebels saying he want to depends on himself and doesn't want to live with him. Sooyoung is a reckless guy and it makes taesung anxious. So taesung use other method to soften him so he would think more about himself. I think when sooyoung decided to box again, he'll accept taesung help. It just he need to speak up.
Why hasn't the MC used the boss-guy to get his knee fixed? He has the money, the place to heal, and can be protected.