Auzzie Oz, are you "in" or "out" of the cult?
The reason I ask is because if you are "out", once he gets married, he will be forced to shun you. Is this acceptable to him?
He is awfully young. What about the girl, is she 17, too? Do her parents know about their daughter's relationship with an unbaptised boy?
It is sad that young ones take their first relationships so seriously. They do tend to get awfully depressed when it ends suddenly, especially if they are talking marriage. And undoubtedly there will be pressure to marry from the elders. You know, they must "avoid fornication" at all costs. Keep the organization clean. No doubt you know the drill.
I figure it might be best to just be a good friend to him and be observant. "Be there" for him. Answer his questions when he asks them. It's nice to see that the two of you are communicating. He does seem to confide in you with his concerns. That sounds like a healthy father-son relationship to me.
I don't know how many 17-year old boys make it to the altar, without experimenting with at least a few dates with other women. Seems awfully restrictive with himself to think the first gal is "the one."
I'm a grandma, so maybe I have forgotten what it was like to be 17...maybe... But I wish only happiness for you --- and for your son, too. At the end of this "thing" it would be nice if you and he were still "family."
Let us know how it is going...
satinka