Yeah, the ex threatens to cause trouble at the cafe about the uke's old job, so Gitae let's the bastard stay but Gitae doesn't stay in the apartment. Its stupid and makes no sense for him to do that until you hear why he didn't go stay with jinwoo
SPOILER
After Jinwoo asks why he didn't jist stay with his boyfriend for a week, Gitae asks "you're my boyfriend? We're dating? Since when?
Yup all this time he didn't think they were in a relationship

i think gi-tae (correct me if im wrong) lets the ex lent his apartment for the meantime because he has a scandal and he’s got no where to go and obviously gi-tae, a big softie, agreed…maybe he’s just afraid to tell jinwoo because he knows he would hate the idea