Understanding a person does not mean condoning; it only means that one does not accuse him as if one were God or a judge placed above him.
Love is a decision, it is a judgment, it is a promise. If love were only a feeling, there would be no basis for the promise to love each other forever. A feeling comes and it may go. How can I judge that it will stay forever, when my act does not involve judgment and decision.
Man's main task in life is to give birth to himself, to become what he potentially is. The most important product of his effort is his own personality. One can judge objectively to what extent a person has succeeded in his task, to what degree he has realized his potentialities. If he has failed in his task, one can recognize this failure and judge it for what it is - a moral failure.