A few things:
A resounding yes to your first two questions, do not leave this issue alone. He is your friend, so take care of him.
What church is he going to that is so "cultish"? It would help to know, so that he might receive more help.
Just love him and be there for him. Pray for him and help him through these tough times, as you said he was experiencing a lot of turmoil. And definitely introduce him to some welcoming pastors (maybe some that are more along the lines of what his church is, but more accepting).
"The one thing truly worthwhile is becoming Godís friend." - Gregory of Nyssa