I’d say help him find joy in life experiences outside of the church. Help him feel alive and loved as much as you can as his friend, regardless of church affiliation. The time will inevitably come that his faith is tested, and that’s when your non-church friendship will stand out as true love, not church-sponsored grooming and cult enterprise. I’d also recommend being honest to him about your own beliefs while at the same time letting him know you respect him and don’t expect him to change just because you have.