I always figured that the arranged marriage thing was just a way to insure that young Vulcans do not die due to Pon Farr. Sort of like if neither has another way to "release," they are married together.
So in TOS, had Spock been boinking Uhura, he'd have just done that and informed T'Pring he is in a relationship leaving T'Pring free to marry Stonn when her/his Ponn Farr starts up.
But who knows? Vulcan mating practices are still not very transparent 46 years after being introduced.
(BTW I do not consider the comics/novels canon)