Responses
Explain that dad went to their place. Remember in when the mom found out, she said the trouble would be the grandpa and her ex husband, but she will protect them... so that was a premonition of the family problem.
Thanks KenGoldenTree and monster94 that helps a lot me remembering things. I remember dad was never around the house so yeah mostly they are divorce.
I think I remember Taesung mom knows about them dating...so why Taesung needs to explain to mom? Or mom mentioned it to Dad already and Dad doesn't like it?