If he likes spending time with you already, you don't have to act any different, fortunately.

I suppose if you were only interested in him in a romantic way, but he wasn't interested in you that way, that could be awkward. But if you just want to tell him how you feel without demanding anything change, I'm sure he'd still want to spend time with you. I don't know of anyone who doesn't like to hear that they make someone happy.