pdsldl Bottom line the Vulcan Reproductive Gland does control all of the parts of Vulcan sexuality. Now that would include bonding and monogomy because when Pon Farr hits a Vulcan is driven to find his or her bonded mate, whether they are married or betrothed. Case in point, Spock wanted T'Pring all the way up to "killing" Kirk only after his Plak Tau was broken could he reject her. Now T'Pring willingly had a complete bond with Stonn for a long time behind Spock's back, and its possible that because Spock is half human the bond wasn't strong enough to hook her. Either way he was still monogomous.
Granted a Vulcan in Pon Farr who cannot reach their mate will eventually have to mate with somebody else but in cases where a completed bond is an issue (like Tuvok) they will try to wait until they are past the point of no return. Even if its using a holo of their own mate.
Vorik was an exception for 2 reasons... A. He was only engaged, and logically concluded that his Fiancee had made other arrangements. B. He mind-linked with Torres, she was his only option after that. Until she beat the crap out of him of course...
These things must have a physical cause, because there are things at work that have nothing to do with cultural mories. Hence why its reasonable to conclude that the Vulcan Reproductive Gland plays the roll in controling all of it. Nothing would make any sense if it didn't.
WG this may all be true but it is your supposition of what you've seen not fact as explained in canon. You are free to interpret these events and draw conclusions but that doesn't mean it's true and should be presented as if they are facts. That T'Pring had a thing with Stonn outside of her betrothal to Spock is established but there is nothing to say she was bonded to him. That the gland controls Pon Farr and making offspring I can buy and even that it has something to do with the bond but Trip doesn't have this gland and he felt the affects of his bond to T'Pol so there has to be more to it. And Spock being monogamous may have to do with males not being interested in sex until pon farr or he may have just repressed any sexual desires he may have had like any good Vulcan was expected too.
In Vorik's case he had no options as his betrothed was not available so it didn't matter. He had to find an alternative and he was attracted to Torres. Spock did the same thing and sought out that nurse during Amok Time because it looked like he wasn't going to make it back to Vulcan.