As far as The Serene Squall vs Amok Time, Spock and T'Pring are betrothed but T'Pring (knowing full well that Spock is attempting a ruse) says that they should terminate their mating bond. One might argue that a mating bond is not the same thing as a betrothal, and like Spock has done many times T'Pring was lying without actually lying. The mating bond and the betrothal are two different "contracts", and ending one is a lot simpler than the other.