Most Helpful Guy
You shouldn't have to pick sides since you love them both! I would ask both your father and boyfriend what happened to find out why your father hit him like that. If your boyfriend is such a respectful and loving man to you, I can't understand what kind of grudge your father has with him. That's not fair to you and your boyfriend for him to treat your boyfriend so disrespectfully like that. It's your choice to decide who you want to be with!
I would get to the source of the problem by talking with your father about why he doesn't like your boyfriend. If you plan on getting married to your boyfriend one day, it would be best to resolve family conflicts first. Usually there's always a reason for people to dislike someone, even if the premise sounds ridiculous!
You love your boyfriend and father very much! No need for this kind of conflict to tear you all apart!