Avoid telling him anything, he needs to see the need to look into it himself, people do this at different times and for different reasons there is no magic bullet...
If it's the "Truth" then it should stand up to scrutiny, right? "Make sure of all things" etc etc
i.e you are inviting him to do some research into his beliefs...
Why dont the JWs want their members to research and check out their own religion, oh that's right, because then they would find it's a cult!