Part one:

After Rin saves everyone from satan, Bon feels as though he can't hide his feelings anymore for Rin, he wants to hold him , kiss him, and love him. Although Rin doesn't know how to answer his confession, even though he likes Bon and think he's really cool.
Bon fell in love with Rin before Satin was trying to take over Yukio's body. It was when they were fighting the impure king.
Rin hides what he's really feeling about a situation behind a smile that shouldn't be there.