The step from platonic to romantic is one way, and one way only - once you attempt to move into that area, there is no realistic way of moving back, things are never the same again.
So - if he is a casual friend, you have little to loose by trying to find out if he is interested. It's very easy.
When you come to say goodbye, make and hold eye contact for a few seonds. Move towards him slowly as though you are going to kiss him. If he kisses you first - you know how he feels. If not, follow through with a kiss on his cheek.
This way yo get to know what your cvhances are, but retain your dignity and fridnship.
Let us know how you get on.