What to do about the boy my dad looks after?

My dad cares for a boy who has special needs and whenever he's over he comes into my room and starts hugging me and kissing me on the cheek and messing with my clothes(pulling my top up, zipping up my jacket) I dont want to upset my dad by saying that i dont want him to come into my room anymore, and obviously i dont want to upset the lad, i seriously dont know what to do.