Would you chalk it up to "it happens" and leave the relationship?
Would you try and improve your appearance in hopes that he/she finds you appealing once again?
Would there be lengthy discussions involved?
Do your answers change in regards to the following parameters?
your SO is your husband/wife
your SO is your husband/wife AND you have children together
(Meaning, it's obviously somewhat easier to exit a relationship from a boyfriend/girlfriend vs. extricating yourself from a marriage/family.)