You're largely correct. Once you discard the traditional marriage model of 'til death do us part,' the situation you cite is pretty much the result. Dalrock wrote an article about this.
Even in business contracts, there's usually some penalty for breach of contract. There is no such thing with non-marital relationships. You're in a relationship until you decide you aren't in one.
Even in business contracts, there's usually some penalty for breach of contract. There is no such thing with non-marital relationships. You're in a relationship until you decide you aren't in one.