Quote 1
“These other armies, they aren't the enemy. It's the teachers, they're the enemy.” (8.126)
Ender’s worst enemies seem to be the childhood bullies he faces; but many of Ender’s friends appear to think the problem is the teachers and the other adults. (This quote is said by Dink, but a similar issue comes up with Petra earlier (7.189).) This sets up the idea that there might be a war between the generations going on here.
Quote 2
He held up a limp hand. "See the strings?" (13.105)
Here Ender is complaining to his sister (during his visit to Earth) about how he’s being manipulated by the adults in his life and has no real options. In other words, he feels like a puppet. Which is exactly what Peter called him in 2.64. Just a coincidence, right? Or maybe we’re meant to draw some comparison between the different manipulators in Ender’s life.
Quote 3
“In the moment when I truly understand my enemy, understand him well enough to defeat him, then in that very moment I also love him. I think it's impossible to really understand somebody, what they want, what they believe, and not love them the way they love themselves. And then, in that very moment when I love them –"
"You beat them." For a moment she was not afraid of his understanding.
"No, you don't understand. I destroy them. I make it impossible for them to ever hurt me again. I grind them and grind them until they don't exist." (13.127-129)
Ender may be a product of war, and he may be very good at it, but in some ways, he’s also a casualty. Think about it. If Ender loves the enemy, then destroying the enemy is always going to be a little painful. (Or very painful.) This is part of why Ender seems like a sad character in this book: the thing that he’s so great at (war) is painful. (Although the fact that we see Ender’s pain but not the pain of, say, Stilson, does strike us as a little odd. It’s important to remember that Ender isn’t the only casualty of his wars.)