Jim Kirk was married to Miramanee for months, and got her pregnant and everything! Jim and Miramanee were obviously very happy with each other. Miramanee obviously loved Jim quite sincerely, and she was a super-decent lady. She was loyal to him to the last, even when her whole tribe turned against him! She courageously took her place at his side while he was being stoned, and this incredible act of devotion cost her her life. It was literally until death did them part. Doesn't that count as a great love!? If not, then what the heck does a gal have to do to rate!?
And why make such a big deal about Kirk's forced kiss with Uhura, when Kirk had a very happy interracial MARRIAGE with Miramanee? He was so ecstatically happy about his marriage to her that he hugged himself at one point out of sheer, pure, unalloyed JOY. I say THAT COUNTS FOR SOMETHING.
Kirk could be a great leader for those people. He possesses all kinds of knowledge that will prove extremely useful to them. He knows CPR for example. He's already in a leadership position: he's starting out at the top. If he leaves her, he'll be leaving all of them. I don't know how many natives there are, but there could certainly be more than 430 of them. What about all of them? Kirk is a responsible guy, and this is a dream job. He's not going to casually shrug off this opportunity.