Marriage is a government construct. So the question is really about the relationship and is the other obliged to stay when they perceive it pointless and unfulfilling.
If you step back and really look at marriage, the divorce rate, those who are separated but not yet divorced and those who stay unhappily married due to it being practical, you will see that there no such thing as unconditional love in marriage.
Because in the end people only act in their own self-interests.
Vows exchanged are irrelevan. Once the interests of one spouse cease to be met the illusion of love is broken, turning the vows into ideals to be met rather than real promises to be kept.
So marriage is really only temporary for many people now. Once marriage became unshackled to religious belief in its sanctity and the potential negative eternal outcome of divorce without religious merit, people begn to chose personal happiness over obligation. This along work divorce being socially accepted.
In the end marriage without social stigma towards divorce is left in the hands of the couple who are no longer "forced" to stay in an unhappy marriage. This means that your marriage is only as successful as the work you put into it and is fueled by how each of you makes the other feel.