Then dump him. You're making replies trying to justify how weird you think it is for people to share food. Sharing food isn't weird. So you say "well they do this weird thing too", okay that isn't weird enough, "well they do this weird thing too."

So dump the dude and move on. You obviously have an issue with his sister, so leave. His sister isn't going anywhere, especially if they're as close as you claim they are.