
Hyesung has the right to be depressed, to want time to be alone, and to think. Sometimes, you've got to let people be for while.
I think telling Byul that mommy is sick/not feeling well would have been better than him seeing his mom then being rejected. But I'm guessing that the plan was for Hyesung to snap out of it/suck it up for the sake of his son.
It is as I said, something was off about that note.