Why must Ender be isolated from his friends? What dangers could arise from having "friendship" with those you must lead? (Chapter 14)

Ender is isolated, so that he will concentrate on his studies and training. It is imperative that he be ready for the war. His friendships change for the same reason. Ender can't base his decisions on his friends, he cannot make decisions based upon what might or might not happen to the members in his squadron. Friendships are based upon emotional bonds, and there is no place for these bonds in Command School... or beyond.