Oddly, I don't really get into emotions at all. That is, my goal is to make the READER feel the motion, and therefore I set up events and circumstances that will cause the reader who is identifying with Ender to feel emotions FOR him.
Not that I never have Ender feeling anything. But the way I do it is to show you what particular events mean to him -- how he interprets them, what he was trying to do, how he tries to respond. Sometimes that includes an emotional response, but I don't dwell on that. I don't try to "write" the emotions; the prose is not emotional. Rather, the prose is unemotional, most of the time -- even dispassionate. That puts the burden of the emotion on the reader.
It's the old theatrical cliche. If someone cries onstage, the audience doesn't have to. But if someone onstage SHOULD be crying, and is trying very hard not to, the audience will cry buckets. Jim Cameron, Leonardo DiCaprio, and Kate Winslett understood this in Titanic, for instance. Leo and Kate aren't crying as Leo dies. They're just cold and scared and thinking about each other. So the audience does the crying.