[cookiecaper]

This is an intentionally obtuse perspective. Marriage is a significant social institution in a way that a mere interpersonal commitment can never be, because marriage is a commitment with a third entity: the community at large.

The social structure accepts and enforces the marital union, providing significant legal protection to itself, the children, and the married partners.

This grants a solid staying power, borne of the subconscious knowledge that no party can really "just leave" and be done with it. This staying power should not be underestimated; it is effective and real regardless of how little one believes they will need to rely on it.

[gehwartzen]

I certainly get that marriage has a social and legal structure which makes it more difficult to split. I just don't think it is paramount to sharing your life with someone. I am married but lived with my wife for 8 years prior and can say, personally, it made no difference in my feeling or commitment for her. During that time I certainly felt I was sharing my life with someone.