I'm datein this really awsome guy named Josh.Well everytime he goes to his dad's he's a jerk.wat should I do?

I really love him but wat should I do? I would take a bullet for him but I dont think he understands me anymore...we have been datein now for a really long time now..but itz like everytime he goes to his dad's house he's always actin like a jerk...wat should I do? please help me.