Thanks for the review! (*does the happy author dance*)
One of the things which makes Kingdom Hearts so tragic (and Kingdom Hearts 2 so much of a relief, in a way) is that the heroes are so young. They're barely started in adolescence, and a lot of the time, they'll still see things as black and white, the way children do. Yet, in the manner of adolescents everywhere, they'll think of themselves as "grown-up", and want to make adult decisions. Being something of a fan of the anti-hero type (and let's face it, Riku is an anti-hero to the core) and having played KH2 before I even got a look at KH1, I found myself drawn to the character of Riku. Playing the two games in reverse order helped, because I got to see where Riku ended up, and then I got to see where he started, which made it easier to trace the arc of how he got from A to B.
As to the matter of Riku's eventual relationships with the other two - it's one of those things about living in a small town, or a small place: the options do seem limited. This is why so many traditional cultures put a higher value on conforming than on individuality - in a small place, all you need is a few rugged individuals, and the order starts breaking down at high speed.