@ur mum I don't think it's only because of what he is wearing. I think all of us can say that Seon-Woo has a low self-esteem. He is not self confident and he is not aware of his actual look.
Moreover there is still this misunderstanding, Jeong doesn't know that he is Seon-Woo's first in everything they doing. So when Seon appreciate all of the small things Jeong is doing for him, he find it weird and it making him think that Seon was hanging out only with bast**** in his past. Also Jeong was treating him really badly at the beginning and Seon was also ok with that. There is just this big misunderstanding and I don't think clothes are the main problem.
Moreover there is still this misunderstanding, Jeong doesn't know that he is Seon-Woo's first in everything they doing. So when Seon appreciate all of the small things Jeong is doing for him, he find it weird and it making him think that Seon was hanging out only with bast**** in his past. Also Jeong was treating him really badly at the beginning and Seon was also ok with that. There is just this big misunderstanding and I don't think clothes are the main problem.