The best way I can put it is this: Yeomin wanted to live his own life, working hard, being accepted for who he is, making something of his own. Then his possessive sex-partner takes over his life, making all his hard work and effort seem like it was for nothing and was rather wasted. He also thought he was in a relationship with someone who mutually respected him. Found out that nope, that wasn't true. Instead of hearing Yeomin out, his possessive sex partner kidnapped him, trapped him in the house, refused to allowed him to see his friends, get his education or be independent by working for himself - all things he wants to do.
Would you not run away if you were being controlled so thoroughly by someone who just throws money at problems to get what they want without taking your thoughts and feelings into consideration???
seriously though, I don't get it why he's running away?