As has been mentioned in another thread, Selar's brother is condemned by their father for having a male partner when he doesn't go thru pon farr, which both suggests Vulcans can have sex without pon farr upon them, and that at least some Vulcans condemn those that do.
Despite how enlightened and intelligent the Vulcans are, they have very Victorian attitudes towards sex, so it is not inconceivable that there would be some more "traditionalist" elements that would looked down upon Vulcans who engaged in: sex with aliens, sex outside of pon farr
, sex with the same gender. That would've made a little more sense than for some unexplained reason Selar's gay brother is immune to his impulses.
Just a thought.