can anyone pls remind me who this ex was and what he did

We don't know yet, it was implied they dated in highschool and that the parents for this guy found out

So far, we know that Garam was having a thing with this guy when they were both in high school. Then the mother of the guy found out and the jerk let Garam take all the blame for their 'taboo' relationship. It broke Garam's heart and from there on he has trust & love issues!