I find it's the opposite. Marriages break up because it's a binary thing; they either get through the "last straw", or they get divorced. Contrast that with peo

I find it's the opposite. Marriages break up because it's a binary thing; they either get through the "last straw", or they get divorced. Contrast that with people in committed relationships who have a sea of grey to work with, and eventually make it work when it could have been a divorce if they were married. I have no data, but I'd bet there are more 40 year olds in relationships of over 20 years than there are married people.