Actually they pretty close when Byulll is younger. And Hyesung has bad relationship with his mother who is Byul's grandmother (he was abandoned by her). But after Hyesung and Dojin live happily as a family, Hyesung's mother suddenly came and apologize. Hyesung still hated his mother no matter what. Dojin somehow let Byul meet his grandmother since he was a child. Also from this Byul know that Hyesung was abandoned. Sadly Hyesung almost did the same as his mother. After he labor, he left Byul and Dojin and makes him take care of Byul alone. Hyesung still has his trauma over his mother. And when Byull and Hyesung fight, Byul accidentally said that Hyesung ever didn't want him. They got fight but I think now they were fine, since Hyesung and Dojin were quite protective.

I didn't read love is an illusion so can anyone explain to me why byuls and his mom don't talk?