I think I’d seen stats somewhere that couples that simply cohabitate rather than get married have relationships that are more likely to end in divorce. Love to find that somewhere...
One thing I have noticed is that couples that have lived together for years and the get married often quickly split up and divorce.
I have several theories here.
1) They got married because the relationship was already going sour and thought that might help
2) When they just lived together they worked at the relationship for fear the other one walked out but once married they no longer saw the need.
3) Again similar to the above but slightly different. When living together they were on the best behaviour and certain character traits were not apparent as they hid them in case the other would find out and leave. Once married though allowed their true character and wants to show through.
4) One of the couple wanted the marriage and the other was quite happy as they were so from word go it caused tension and every row it was bought up. Nowadays this is often not the woman. In fact I know of 2 long term commited relationships where the man would love to marry the woman but she will not due in one case to an unhappy marriage and guilt of how much was spent on the wedding and knows that her mate would not just settle for a quiet registry office do and small party for friends but because he has not been married before feels he owes his family a big do whereas she would marry him if they could just do it quietly with intimate friends. The second one freely admits though committed and loves her partner to bits and they have 2 children in their late teens together that her first husband was the love of her life and feels she would be short changing her partner of well over 20 years if she married him - crazy I know.
5) And again related to the above reasons when you marry someone and then start living together you discover things about each other and work them out as you go along. If you are already are living together you already know the things that annoy you about your partner and if the marriage makes you least likely to worry about annoying your partner that could well lead to breakdown of the relationship.
They would have nothing in common with the average single who goes to the night club or a singles bar most weekends or pursues activities that either a family could not afford or would not be suitable especially for the younger children.