Ender is a wonderfully created character. Card did an admirable job of making Ender both dynamic and round. He is a character that we love, hate, admire, and feel sympathy for at various points in the story.

For the textual reference regarding Ender admitting that he hates himself, check chapter 13. A lot of important dialogue happens in this chapter between quite a few characters, but you are looking for the sequence that has Ender speaking with Valentine about his efforts to win the war. At one point in the conversation, Ender admits to his sister that he has been trying to figure out why he hates himself so badly. Valentine tries to stop him from thinking like that, but Ender pushes on and explains that his hatred stems from his love.

Ender understands that in order for him to be victorious against any enemy, Ender has to fully understand that enemy. Ender has to understand the enemy so well that he essentially loves them. It's at that moment of love and understanding that Ender destroys his opponent. He hates himself for being able to completely wipe out that which he loves. He sees that this ability of his is on par with or even worse than what Peter is and can do.

So even Peter might be a better alternative.