Is this common for JWs? - Yes, especially those mentally hooked by Watchtower.
This admission is a symptom of bleeding the false god - Watchtower.
My suggestions / advice (you are not pressured to follow, freely choose any or none):
You may suggest to him to look around, and investigate if the "voice of the stranger" (outside Watchtower) has truth. Part of Watchtower's mind-control tactics is to control vital information.
Let him "test out his faith" outside Watchtower in the real world. Let him examine some websites such as http://www.freeminds.org
Let him secretly question Watchtower control. Of course, unless he is absolute ready to change and leave, he may openly question others, then probably face either expulsion through disfellowshipping or voluntary dissassociation.
Others remain inside as secret dissidents for a cause. If he likes to really test-out his faith and reasoning from scriptures then he may check-out http://www.carm.org/jehovahs-witnesses and secretly/anonymously join the discussion forum for Jehovah's Witnesses. There are vigilante JWs there trying to witness to the mainstream Christians. As long as he is anonymous there he can openly express his thoughs and reasoning without fear from Watchtower. I look-out for such in this forum. The topics I would mostly post is anti-Watchtower. Most are currently anti-JW in this forum.
Caveat: the risks are the same when discovered by policing forces : "repent or face expulsion through disfellowshipping". When one leaves Watchtower control, they have to be mentally ready (because of the mental hook) to be designated as Apostate by Watchtower.
All leaving Watchtower control need support group help.