In John Knowles's A Separate Peace, why was Gene hiding his emotions from Phineas?

Although Gene
and Phineas are best friends, Gene hides his emotions because he doesn't trust the relationship
due to its competitive nature. Gene is intimidated by Phineas because Finny is charismatic and
athletic. Finny can get any adult or student to do what he wants them to do or agree with him on
any topic. Gene is more quiet and academic-driven. Because of this intimidation, Gene tends to
project those insecure feelings onto Phineas and to believe that the unspoken competition is
more than it is. Consequently, Gene is caught off guard when Phineas tells him that he is his
best pal while at the beach. Gene doesn't say anything back even though he thinks he should have
later. Again, due to Gene's insecurities about the equality and loyalty of their friendship,
Gene isn't easily moved to share his feelings. And, Gene doesn't seem to realize the importance
of his friendship with Finny in his life until after he breaks Finny's leg and must face life
without him at school for awhile. He also doesn't understand their friendship until the end of
the book when forgiveness and clarity are finally achieved.