Playing Devil's Advocate Here: Maybe Gale knew he could never truly make Katniss happy. Even though he may have loved her, letting her go was his truest way of saying, "I love you."
------------ “True love doesn't have a happy ending, because true love never ends. Letting go is one way of saying I love you.”
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“True love doesn't have a happy ending, because true love never ends. Letting go is one way of saying I love you.”