What is the significance of Ender making friends with Alai?

Ender thinks that Alai's whisper of the word "Salaam," and his kiss on Ender's cheek, might be a part of some forbidden or repressed religion. Ender remembers the only other time someone showed such sensitivity to him, when his mother prayed over him when he was just a baby. The word "Salaam" literally means "peace," but in this book it is used in a special context, suggesting tenderness between two best friends. While Ender does not know what the word exactly means, he realizes its importance to Alai, and he sees its significance for their friendship. "That was what Alai had given him; a gift so sacred that even Ender could not be allowed to understand what it meant." Ender thinks that after something so sacred, nothing can be said, so the two best friends share a look of understanding and then Ender leaves. This moment, like Ender's departure from Valentine, is one of the most heart-wrenching scenes in the book. Ender and Alai, at this point, share a deep friendship, and it is a shame that Ender is being made so independent that he will not be able to maintain the friendship later. In the place of Alai, but in a much lesser quality of relationship, Ender becomes friends with Petra. Ender and Petra also train together, and their friendship tends to be more instrumental.