I love that Ron truely cares about Leslie in a loving way, but as a friend and is okay to admit that. Rather with Diane he shows romantic love and is also okay to admit that, but shows it differently like in this scene. I wish more shows would demonstrate caring/loving isn't always romantic between a guy and girl, it can be a friendship kind of love.
One of the best scenes/episodes of this series shows his acknowledgment for how amazing and important Leslie is to him, but also subtly shows Diane He loves her very, very much. This show is a masterpiece!