How do you know that Peeta's feelings for Katniss are real?

For much of the book we don't know how real Peeta's feelings for Katniss are. Like Katniss, we wonder if he is merely playing her. I don't think we know for sure until Peeta risks his life and defects from his alliance to save Katniss from the killer bees.

I gotcha. Now I know much more.