Could it be that you are that stable guy that came along when she needed to feel safe? You don't sound like a party-guy (that's NOT an insult). How/when did you meet? Were you one of the rich guys at the country club?
Were her A's with guys who are party-guys?
How much does she drink? How many days a week, how many drinks, what is she drinking?
When she "parties," is it at home with you or is it out?