The envy Gene has for his friend and roommate Finny shows up most of the time as jealousy in A Separate Peace by John Knowles. It is true that Finny is just one of those guys that everyone knows and is attracted to because he is innately good, despite his constant rule-breaking. He is someone who is good at everything, including getting out of trouble. It is not surprising, then, that Gene sometimes envies Finny; nor is it surprising that often that envy becomes jealousy and turns eventually into resentment.
Finny nearly always manages to escape punishment for breaking the rules, and Gene (who is innately a rule-follower) envies that.
I was beginning to see that Phineas could get away with anything. I couldn't help envying him that a little, which was perfectly normal. There was no harm in envying even your best friend a little.
Eventually, though, Gene's envy begins to grow into an animosity, and there comes a time when Gene begins to hope that Finny gets caught (and presumably punished) for his often outrageous lies.
This time he wasn't going to get away with it. I could feel myself becoming unexpectedly excited at that.
When Finny breaks a school swimming record without any training and then does not want anyone to know, Gene finds it hard to believe that Finny's motives are pure, probably because he knows his own heart is not as pure.
Was he trying to impress me or something? Not tell anybody? When he had broken a school record without a day of practice? I knew he was serious about it, so I didn't tell anybody. Perhaps for that reason his accomplishment took root in my mind and grew rapidly in the darkness where I was forced to hide it.
These things all begin to fester and grow in Gene's mind, and soon he has moved from envy to jealousy and finally to resentment. When Finny keeps insisting that Gene be part of the Suicide Society, Gene assumes Finny is trying to keep Gene from studying so Gene will get grades as low as Finny's. It is not true, but Gene believes it. Finny just assumes that Gene will go with him to the tree, and Gene says,
But examinations were at hand. I wasn't as ready for them as I wanted to be. The Suicide Society continued to meet every evening, and I continued to attend, because I didn't want Finny to understand me as I understood him.
Ultimately, of course, this internal resentment turns to bitterness for just one moment, and Gene jounces the tree limb, sending Finny to the ground.
What is apparent in this relationship is that Gene ascribes all of his own suspicions, enviousness, jealousy, and resentment to Finny, assuming Finny thinks and feels as Gene does. In fact, however, the two boys are nothing alike and Gene misreads everything about Finny.