Re: James, how could you ever get involved with a nut like Janice Lest
Nah, it's more simple than that. Lester was obviously career-driven like Kirk was (a recurring theme in Kirk's women) and their relationship "ended badly" when Kirk returned to Starfleet. Basically, she ws a psycho-bitch (the relatively normal kind) to begin with, which evidently surfaced when Kirk left back for the fleet. ("Your world of starships doesn't include women" takes on a more significant, and realistic, meaning if you realize she was badmouthing Kirk alone, after all.)
Dr. Lester carried basic resentment, which magnified as Kirk became more and more legendary in his exploits. We also know that her resentment and animosity was selfishly enabled by the man who 'loved' her in the episode (forgot the character's name) so much that he was a more-than-willing accomplish to her insanity.
Basically, she was in an echo chamber that kept reassuring her growing insanity, years after someone would have come along to say "grow the hell up, already" in a more normal environment. But she was isolated with a man with vested interest in coddling her up... creating the crazy we all know and wince about.