Most Helpful Guy
I say talk to your sister about it. If you want it or don't want it. It sounds like you kind of want to, but are unsure. Of course I could be reading that wrong.
If you really hate the idea tell your sister and call him a creep next time you see him. Your sister will tell him why you don't like him any more.
Most Helpful Girl
Depends if you want it and sounds like you kinda do or if he tries to force it with you. Maybe tell your sister or something.