What do you tell parents who think your bf only wants you for sex?

I know my bf better than them ofc. They’re only seeing things from the outside and it’s not even what they think at all. He gives them no reason to even think that. My stepdad and mom only think that because according to them, every guy my age wants that. I’m 17 btw. They’re kind of hardheaded but I want to at least crack that shell a little bit. What should I say?