Tell him what your telling us. That your unsure about the whole thing because you shouldn't do anything you aren't comfortable with. He should understand and it isn't a bad thing to take things slow. Go as fast as you wanna go
It has to be your choice but if you are asking the question then you have doubts. You must feel excited about it. I have been intimate with many guys that I like and the ones that I dont like never get a chance.