QuietUnobtainable

I can 100% still dislike him bc he knew what he was before he started dating her. And as an Aro or ace, you disclose that to your partner always bc romance and sex can and will always affect a relationship especially for ppl who aren't aro or ace. It's a hard talk but if you expect them to be your partner

Judging by the way the Ex's friend talks about how Yoomin will come running back in Hyeondu POV chapters i have a feeling that's who was on the phone.

However, a massive betrayal would be the sister. Not likely but it would Sting and also be a good way to have her want to remove all strings attached to her Ex.