Oh my gracious, sit your partner down to watch the scene between the Romulan Commander and Spock in The Enterprise Incident. And tell them to be prepared to lose that pinkie bet! 🙂
Here’s some background on what has come (in fandom) to be called the ozh’esta (the finger kiss):
The first time we see the “Vulcan kiss” gesture it is in Journey to Babel (the episode you reference in your question), where it wasn’t actually written in the script. The actors playing Sarek and Amanda asked Leonard Nimoy about the body language and gestures used by Vulcans, in order to give their performance continuity with what had been developed in Star Trek so far. It was Leonard’s idea that hands and hand gestures are deeply significant to Vulcans, and between the three of them the actors worked out the now-familiar two-finger touch as the way a Vulcan would interact with his bond-mate.
Then fan writers – rabid as ever to develop the full backstory (and bedroom story) behind every thing given us on screen – took over. Essays and fanfiction quickly developed the fannon (fan-made cannon) that we are familiar with today: the gesture is the Vulcan equivalent of a human kiss; it’s a touch through which the telepathic bond crackles like lightening between a bonded pair; Vulcan hands are erogenous zones that one only fondles in private.
Gene Roddenberry was extremely aware of and respectful towards the development of fannon in the early years of Star Trek. He bought the fan zines that were in circulation at that time, he kept them in the production offices, and he insisted that the show writers read them and keep them in mind when writing new episodes. (These were golden years for being a fanfiction writer, needless to say. GOLDEN.)
As a result of Gene’s requirement to read fan fiction, show writer Dorothy Fontana was fully aware of the fannon about Vulcan sexuality when, during the 3rd season, she wrote The Enterprise Incident. During pre-production, the new producer on the show (the unfortunate Fred Freiberger) went and added a rather torrid love scene between the commander and Spock, very much against Dorothy’s wishes. Infamously, the scene called for (and this line is burned forever in my memory) Spock taking her in his arms and “raining kisses on every square inch above her shoulder.” (!!!!)
Well, Dorothy, god bless her, pitched a fit and refused to back down. Pointing out that the fans “know exactly how a Vulcan makes love,” she insisted that Spock and the Romulan commander be seen fondling each other’s hands rather than raining human kisses on faces and necks. Leonard found out about it and balked at playing the scene, and wrote his objections in a now-famous letter to the production heads. Dorothy and Leonard prevailed on this one, and if you go watch The Enterprise Incident you will see quite a racy (for Vulcans) scene play out between Spock and the Romulan commander – all expressed via the touching of hands.
I hope that helps. I’m trying to think where to point you for source material, since I’m writing this from memory. (For ten years we only had 79 episodes to obsess over. It shows.)
You could check These Are the Voyages by Marc Cushman and Bjo Trimble’s Star Trek Concordance (but be aware that there are some errors in it); most or all of these details are probably referenced in those books.