If he truely cares for you, he will be understanding. He may not totally understand the FULL MENTAL context of what it is like being a JW, but he will be a shoulder to lean on. And I highly doubt he'll be overwhelmed. Most "wordlies" don't give a rat's a$$ about JWs and their beliefs. Not in a rude way, but they honestly don't put as much importance on it as the society makes JWs blieve.
I know for myself, with my own fade, I would not have been able to do it if my boyfriend at the time was not such a great listener. I told him I felt as if I was using him as a crutch, but really he was lifesaver. It took so much of me just to open up and get out of my own head. I was paranoid about a lot of things. Sometimes he would chuckle and giggle, or straight out laugh at some of the things I was so serious about. That would make me so mad, but then again it helped me realize just how silly being a JW is and was, and the things I was paranoid about really didn't hold any merritt.
Tell him the truth. You'll probably feel a great relief after you are done being open and honest with him.
Good Luck and Happy Fading!