I think marriage is pretty well defined. The problem these days is that the roles women play in society are changing, and women are becoming more empowered. This means that many more women refuse to accept the role of follower and leave the decisions up to the men. Advertisers do their very best to profit from the differences between the sexes, by giving easy credit to women, stressing that products be sex-related (men's and women's deodorant, soap, home decorator accessories, cars, even trucks. Everyone is told that they can ans should afford the very best and most expensive products.
There is a sexual magnetism that takes place between a man and woman when they first meet. This rarely lasts longer than three or four years, and almost never past the birth of two children. After that, either the children provide a lasting bond, or they don't. When the children move out, another strong force to separate can occur. It is not normal for a majority of human couples to be attracted to one another for life, no matter what the churches say to the contrary. If they are it is wonderful, but it is also rare. Guilt and social pressures are a major force holding many American couples together. In small towns and established neighborhoods these forces are greatest, and in bedroom communities like suburban Las Vegas they are weakest.
Most of the forces that unite straight couples have the same functions among gay couples, it seems to me.
