Yeah a large part of me knows that's true but Kirk almost shagged Noel on the Sick Bay photocopier at the Christmas party so who knows what might happen in a moment of weakness?
He did nothing of the kind. I'm amazed how many viewers mistake fantasy for reality here.
The whole point of that sequence was that in real life,
nothing happened between them beyond a very minor flirtation that Kirk felt embarrassed about after the fact. That's why they could "be sure" that the implanted memory of a more intimate interaction was false.
And let's not forget later on -- even when Kirk has supposedly been brainwashed to feel overwhelming love for Helen, he's still able to shake it off with only a slight reminder of his duty, and within a minute he's quite callously sending Helen into a very dangerous maintenance duct full of lethal exposed cables.
First-season Kirk was not the Lothario he's stereotyped as today. Look at "Mudd's Women," where he was the only man other than Spock to be essentially unaffected by the women's enhanced allure. The original idea behind the character, the idea that prevailed through the first season and less so later on, was that he was a totally dedicated military man, someone who placed his duty above all personal concerns. The only times he strayed from that, usually, were times when he was under some kind of mental influence or otherwise not himself.