I'm dating this man over 5 years now

I am dating this man and he has a step son the other day we were driving and he his stepson called him so my bf answered and they started arguing through the phone. My bf starts calling his step son illiterate, retarded, stupid , son of a bitch, ignorant. And I was in shocked 😱 and frightened. I told my bf he should not talk to his step son like that and should be the bigger person. My bf was mad he told me I'm sorry but this boy gets in my nerves. I told him I didn't know this side of you. I didn't know you talked to your children like that. He raised this boy since the day he was born. His step son is 22 years old and bf is 57 years old. Should I leave the relationship? Should I stay? I am 27 years old