He doesn't allow it because then In Seob will leave him. And knowing his thought process, if that ever happens, if he has to kill In Seob entire family to make In Seob be with him, he will do it. He knew he's too mess up to be the obvious choice that's why he wouldn't give any chance or opening for In Seob to be anywhere that's not with him.
His way of expressing fondness and liking In Seob is very mess up. But I guess reading the novel and reading the manhwa I can understand why he's like this although he's mentally not at the right place like normal people. Later in the chapters when he come to realisation how much he fond In Seob and not just obsessive about him, he actually try to compromise a lot of things because he thinks that's the best for In Seob. He also admits that In Seob will never iniate anything with him and it does makes him feel shitty. It is also something he can live with as long as In Seob will be by his side.
Like, why don’t we all go see his mom? Like y’all are already technically in America. Just let him go over there and visit. I doubt he’ll say anything to his parents.