It is a big deal because he is literally manipulating and playing around with Jun while he is living it up. Look, I think I have had this convo with you about this comic before and I don't wanna repeat the same convo with the same person. I know you like Silon, which is fine but I don't. Let's leave it at that.
If it was irrelevant to the plot, it wouldn't exist in the manhwa at all, what? Him sleeping around solidifies the fact that he does not give a fuck about Silon while Jun does. I don't know why you are hellbent on finding some malicious ulterior motive behind my comment, man. Let's agree to disagree. Again, you are free to enjoy his character as you like, I am free to dislike him for whatever reason I want. He doesn't exist and isn't gonna be hurt by it.
I don’t think Silon playing around way before he even met Jin or Jun is relevant bc it was only mentioned once at the end of s2. Maybe the part that jun never dated/virgin could(?) probably be a way to show how naive he is about that stuff & how easy it is take advantage of him. And as I said again, I’m not excusing Silon’s actions & I don’t care if you dislike him or whatever.

Silon is one of the trashiest MLs I have come across. He does not deserve Jun, honestly. Jun needs to save himself from Silon's games and move on or at least there NEEDS to be a long chasing arc before they ever get together if that's how it's gonna be by the end. It doesn't feel fair how Silon gets to sleep around while Jun has to be a pure maiden waiting for Silon to have sex.