Use three points of supporting evidence to compare and contrast Gene's and Finny's thoughts on friendship.

I think a key point to consider is the fact that Gene thinks horribly of Finny regularly, but any time Finny has even a flash of a negative thought about Gene, he apologizes for it and shakes it off.  Here are some example quotes you may be able to use:

1. Gene (p. 17):  "Why did I let Finny talk me into stupid things like this?  Was he getting some kind of hold over me?" (this is when Gene jumps out of the tree for the first time, after Finny's peer pressure has gotten him into it)
Finny (p. 51):  "You never waste your time.  That's why I have to do it for you." (This is Finny explaining to Gene why he's always trying to get Gene to do crazy things; he wants Gene to have fun and feels responsible for providing that fun.)
I think the above set of quotes illustrates that Finny feels like their friendship is solid, and he wants good things for Gene.  He wants Gene to have fun, to loosen up, to enjoy his youth and the "separate peace" in which they live.  Gene, on the other hand, is suspicious of Finny's friendship, and can't see the positive side of the things Finny does.  He only sees Finny trying to get him into trouble, or Finny managing to avoid getting in trouble when he should be.

2. Gene (p. 53):  "It was all cold trickery, it was all calculated, it was all enmity." (He is speaking of Finny's friendship with him.  This is the point where he "figures out" that he and Finny have been competing all along, jealous of one another's successes.)
Gene (p. 59):  "Now I knew that there never was and never could have been any rivalry between us.  I was not of the same quality as he."  (Now Gene realizes that HE was the jealous one, the cold/calculating one; Finny never was.  He understands now that all of that negativity he has been feeling was of his own invention, not caused by anything Finny has done or said.) 
Now Gene knows that Finny is a genuinely nice person, a true friend.  He hates that, because it means that he was just the opposite.  Shortly after this is where he bumps the tree limb to make Finny fall.  We see a similar realization later, when Finny falls down the stairs.  On p. 179, Gene says:  "Once again I had the desolating sense of having all along ignored what was finest in him."