SPOILERS. Arthur's feelings for Tom.
There are some wonderful relationship issues in this... I've been pondering on that of Arthur and Tom. Tom obviously looks on him as a friend, a friend he cares a lot for, but no more than that (although Tom's tears at Arthur's bedside and his tears and physical anger after his death might suggest otherwise). Whereas Arthur for Tom is a more difficult one.
Obviously at Arthur's age, true love is uncommon, but exists nonetheless. Obviously we're not talking in sexual terms here (I'm not a pervert, honest! :) ), but I think that Arthur's feelings for George go stronger than just a friend - note the letter to his parents, his conversation with Tom... Although it could also be a simple/innocent schoolboy infatuation.
On a different note, I think that they shouldn't have killed Arthur. Their relationship later in the book is key Tom's development as a person. What d'you reckon?
Donna: You just want to mate?
Dr: I just want A mate!
Donna: You're not matin' wi’me Sunshine!