At the best of times, friendships between children sometimes require some intervention from adults to keep things civil. In an environment like that faced by the characters in Lord of the Flies, where there are no adults, no guarantees of a safe future, and no certainty as to where their next meal is coming from or whether they will ever be rescued, friendships are a difficult thing to sustain.
While the littluns are often portrayed as sticking together, possibly forming some semblance of friendship between them, the relationships between the older boys are fraught with difficulties, and cannot be described as any form of friendship.
While Ralph is originally declared leader, he is constantly undermined by Jack, who can in no way be considered a friend to anyone. Jack's unfriendly ways can be seen throughout the novel, such as when he abandons the signal fire (thereby missing out on an opportunity for rescue) and carelessly breaks Piggy's glasses.
Simon is probably the friendliest and most rational of the lot, but it doesn't get him far. Slowly the boys fall under Jack's version of leadership, and when Simon rushes back to tell the boys that the "beast" is definitely not real, the boys, who by now are in some sort of stupor, think that Simon is the beast, and his friendly act of coming to tell them that there is nothing to worry about results in his death.
However, it must be noted that there are some signs of friendship. For example, Samneric eventually warn Ralph that Jack and his pack of hunters are planning to hunt him down that night. Luckily for Ralph, their plan is interrupted by the arrival of a naval officer that heralds the boys' rescue.