A straight-laced, returned sister missionary, raised in the cult, and in family of similarly entrenched cult members, will not likely remain happy with a non-member. He said that if there is an exception, it is for the individual to obtain through the spirit.
I agree with what you and so many of the other replies have said: Listen with an open heart and curiosity.
We would have a movie night at his apartment on a Saturday night and the next few days would be great. Mormons are also taught "Families can be together forever.