How do I tell him that I care about him with out scaring him?

I've been seeing this guy, and he keeps saying how he doesn't get why I care about him so much.

When he asks I've just been saying "Because I do".

I wanna be able to tell him in a more heart felt way but I don't want to scare him off by telling him how much I love him.

So how would I tell him how much I care about him with out freaking him you?