@Ceereus I think this is partly her fault for not cutting him off her life. I don't know whose idea it was to stay as friends, but that must've given false hope to both parties. After chapter 19 I came to the conclusion that deep down Jiyoon was waiting for Gaeul to change his mind and settle down with her just as much as he was expecting her to give up the idea of getting married. It's crazy how she's never even considered cutting ties before, and I think the reason why she's so upset over their breakup again, when she should be over it, is because it's finally sinking in that he'd give up anything to achieve his dreams, but when it comes to her, he can't make any promises.
As for how he's all flirty and affectionate, it makes me wonder if he wasn't always like that, even when they were just friends in college. Back when he asked to sleep at her house I honestly thought: "what a piece of trash, he's trying to get back together just to freeload since he can't pay his rent". But no, he only stayed there for one night. He also immediately left the other friend's house when he realized he was being a bother. Then I thought: "ok, so now that he has absolutely nowhere to go he's obviously gonna beg Jiyoon to stay at her place for a while", and I was surprised yet again when all he asked was for her to go to his show. It was there that I realized he wasn't as irresponsible and untrustworthy as I first thought.
That's why I'm still on the fence about whether or not he's purposely trying to change her mind because he doesn't care about her feelings or if this is a combination of him being hopeful that he still has a chance with her and his naturally flirtatious personality and because he genuinely can't understand why marriage is such a big deal to her in the first place.