It's been implied more than explicitly told but I understood that when their parents found out they were together at school, the ex probably blamed him. Probably some crap like "he was forced" or that the gay was Garam and he tried to stop all his advances.
While yes it is disappointing, it comes into play later in the story as to why he came back that way. Not going into details, but it has to do with the King’s hearts guys.
I just want one of them to confess idc anymore who and how just asap it's so frustrating