he's got the Defender inside (like Intel, but better)

HAH that actually made me laugh out loud.

Again, I think many things you've mentioned have explanations - but that doesn't mean you have to like it. I mean, if I kissed someone and there was a sort of telepathic connection, I bet a good part of my attention would be on that, not just on the kiss (unless he was a REALLY good kisser, I suppose, and most guys I've kissed aren't that good, especially the first time). I always saw Ronan's anger and twitchiness throughout Abroad as a combination of him fighting with the Defender and the Defender fighting to come out and, well, fight something. The passivity during the battle at the end was another aspect of that battle - he knew that if he fought, the Defender would become truly part of him, instead of just an extra bit waiting to emerge, and he had no idea what that would do, what he would become, if he would still be him on the other side. Doing nothing was a way to put off the inevitable time when he would be changed, one way or another. And yes, that's selfish when the whole world is at stake, but he's a teenager, for one, and for two...when it's your life, it can feel more important than the whole world.

I do agree that it wraps up quickly, though, and the resolution could be more thorough.