Taesung has the desire to lock him inside because he wants to cherish him and not let him get hurt. Despite that, he didn't lock him in and gave him freedom. Soo young is living on his own in his house and also has a job he choose by himself. Taesung is possessive but not that possessiveness that turns into violence. He is different from the ex.
My point is, that all comes with the condition of SooYoung being tied to him, and his volatile nature. He’s not doing it out of the pure goodness of his heart, he’s doing it for the endgame of SooYoung being worn down enough to just give in. Everyone one wants something from him, nobody just wants him, and the one character that seems to just want him also sexually assaults him so.
When you said he isn't doing it from the goodness of his heart, what is the reason then. Taesung is a mafia and handsome guy that can get any person he wants without begging or being nice to them. Soo young being a debtor is enjoying the benefit of taesung liking him. Taesung could have beaten up and force him to work under him to pay the father's debt treating him like his other employees. Which debtor talks back to their creditor and chooses how to pay for his debts.
I knew what to expect but I still didn’t want to be faced with it. This story is clearly inspired by Finder which makes me incredibly sad, SooYoung deserves so much better and even though TaeSung(?) treats him a bit better later on he’s really no different from his “ex” who just wanted to keep him in his home as a means of controlling him. In stories like this it’s never an option, but I would like for SooYoung to be alone and free to do what he likes, without any obligations to men who only manipulate him and treat him like property before his own person. ╥﹏╥