I hadn't thought about this episode in a while, thanks for bringing it up Zap.
I too can't fault Kirk for falling in love with her so quickly, akin to Kirk falling for the Dohlman of Elas with the help of her tears. Rayna was perfection in so many ways, so very easy to be mesmerized by her. I know I would've been puppy eyed straight off.
But yeah... it wasn't a drug acting on Kirk, just his male sensibilities. You have most of your crew knocking on death's door, but you can compartmentalize it and enjoy some pool and passionately flirt with a woman? Yeah, looked really bad for ol' Jimmy boy. I'm surprised McCoy didn't make more of a stink about it.
About the ryetalyn imperative... Kirk and party are very sensible people. Here's Flint with his very own planet and time without end at his disposal. It was SO BLATANTLY CLEAR that the ryetalyn would be a mere spec of inconvenience to Flint. This wasn't a precious resource for him in any shape or form. Kirk knows that the ryetalyn is possible to retrieve and here's Flint getting in his way. I don't blame him for taking a threatening stance, after having offered compensation (to which Flint replied "You have nothing I want."). So, Kirk was stuck in a Catch-22 scenario and desperate.
But of course, Flint eventually recognizes the advantages of having the men there, to help lift Rayna to the next level. Only, his superior intellect managed to overlook some of the obvious concerns. At least to anyone else. Flint was so arrogant, he couldn't see the danger. Of Rayna perhaps falling for some other man and that her relationship with Flint had really been forged as more like father and daughter.
This episode is one of my favorites for many reasons. I try to overlook Kirk's ridiculous behavior, chalking it up to the stress of the situation (the loss of his crew) plus perhaps being well overdue for some shore leave (a persistent problem with him). What I also found a bit offensive was the tediously PRIMITIVE works that were supposedly hand written by Brahms himself. Um... WRONG. I am familiar enough with the work of Brahms to know that the trite waltz we heard Spock play was nowhere near anything Brahms had written (one would have thought a little research and some cleverly written waltz by a modern composer with obvious elements from the style of Brahms could have been used). But again, that can be overlooked. James Daly did a terrific job with his role. So did Louise Sorel with hers. While a simplistic episode from a set and effects perspective, it was a refreshingly interesting story with a surprise kind of ending.