Like it was mentioned above, see how she deals some of the issues now and if she can't handle it, it might be better to find someone else. These garments will not be fun for dating, if you know what I mean. Talk about issues with Jehovah's Witnesses etc.
Should I just end it if the loneliness bothers me already. Also, as Joanna points out, men and women already inhabit a separate culture. She will insist on raising her children in the Mormon church. Interfaith marriage is but one variety of the learning experience. Many men have begun leaving the Church in their early twenties as the mission has become more important. You've made good points about not bringing up the CES letter or anything that could be called "anti-mormon. And now he is in his 60s.