In the last paragraph, what keeps Gene from responding in kind when Finny says that Gene is his best friend?

Gene's reluctance to answer Finny's comments that Gene is his best friend foreshadows some kind of conflict within Gene; up until this point, Gene has had nothing but praise for Finny, but the fact that he cannot acknowledge his best friend openly indicates something wrong beneath the surface. Gene says that he was "stopped by that level of feeling, deeper than thought, which contains the truth"; Gene finally acknowledges his second thoughts openly, which foreshadows Gene's coming crisis about his true feelings for Finny (40).