Try your hardest not to get emotional. Tell him you have told him the whole truth, and if won't accept it and needs to leave, that's his decision and you'll respect it. It's hard, but you have to detach emotionally and let him make his own decisions. Begging, crying, and pleading will only drive him away.
The LORD is near to all who call on him, to all who call on him in truth." (Psalm 145:18)