It's a double edged sword, I guess, how Chanyeol decided to break up with his gf. On one side, he wasn't honest about his hobbies, about why he really didn't want her to bring her home, etc., and I'm sure as hell that there's some chances that she could have adapted to it... I mean, it was a 4-year-old- romantic relationship, you have to be honest with your s/o at that point, because communication is important in a relationship.
However... the girl also showed her colors when the first thing she did when they both reunited (a month after they got into a discussion and stopped talking to each other) was ALMOST slapping him? I mean... when I first read that bit, I got this whole idea that maaaaybe this was a bit usual in their relationship... which is also some red flag. Of course, maybe I'm going a bit ahead of myself, since we don't know exactly how well was that relationship in the first place, we only have context about the moment they were deep into toxic interaction with each other.
I think some ppl forget that there may be another layer of why Chanyeol was being hush-hush about his make-up hobby (and blog/youtube), and that's also thanks to past trauma (which we find out is not part of this flashback), not saying it is still justifiable to see how he acted (and has been acting), but it's still understandable in how he is. How he doesn't interact that much with others with obvious exception of Haedam, and how this noisy girl is changing him (quite slowly but).