Do Your Homework
If your betrothed has siblings who you're comfortable navigating sticky subject matter with, consider them valuable sources of insider intelligence. They'll know (or at least suspect) why your man's relationship with his mother is so involved. Brothers and sisters can be a gold mine of information. And you don't have to put them on the spot by asking why your guy can't seem to let go -- just ask questions about the mother/son dynamic in the family, and you're likely to learn a lot. Finding out that the man in question breast-fed until age 5 is possibly all the explanation you'll ever want or need!