@XXSpadeMasterXX,
This is Exactly what I would say, presuming he is NOT ill, and truly "feels" he is the Messiah....and was looking for spiritual evidence from God through me to Him....
In your life, By your actions, DO you totally CONTRADICT EVERYTHING spoken about Christ in the Scripture? Examples: DO you sin? Were you born of a Virgin Mother? Have you ever Physically been to Heaven by your Own power?? DO you "know" what the Heavenly Father Looks like? Are you able to greet people who die. and reach for you in "your kingdom"?? Have you or do you remember being Crucified? (and having stigmatic or ecstacic experiences, IS NOT THE SAME) etc...and if he genuinely answered No but it's not that way....then I would explain to him, he may very well be faithful to Christ, but if you proclaim your Christ, and your not in the end, and are a False Christ, then to God (again presuming he is NOT ill) that is worse, than not believing now, but in the end accepting Christ....in other words, whether your faithful to God or not, if you in fact are a false Christ, then you in fact are MORE entangled, and WORSE OFF, than being the simple of the MOST simple, and excepting Christ, rather than proclaiming you are
THE Christ....that is how I would approach him in conversations about Jesus, himself etc....