Finny says that if u love something it has to love u back. Gene realizes it isn't true, & decides to give it a chance. What is the significance of...

After Finny's comment, Gene doesn't really "decide to give
it a chance" at all at that point.  Gene acquiesces and simply allows Finny to believe
that he agrees.  This is yet another facet of Gene's betrayal, the lack of true
connection, of honesty in communication between the two of
them. 

Gene hears and evaluates Finny's comment about love,
but decides that Finny is persisting in his fantasy world.  Gene admits that "in his
seventeen years of life"  that idea of loving something and it loving you back "in
whatever way it has to love" as Finny states, is simply not
true. 

But rather than engage Finny in an honest and
open conversation on this topic, he apathetically dismisses Finny's statement as "every
other thought and belief of Finny's", as something that "ought to be true."  This shows
an element of direspect from Gene.