Love NEVER justifies sin

“[Love] does not rejoice in unrighteousness” (1 Cor. 13:6). 

Love never justifies sin.
To most Christians, the idea of rejoicing over unrighteousness is repulsive because it suggests enjoying deliberate, wanton sin. We’ve seen sin’s tragic effects on mankind and know how it offends God, so how could we ever rejoice in such a thing? But rejoicing in unrighteousness includes any attempt to justify sin in your own life or in the lives of others, and this can be a very subtle thing.
There are many ways to rejoice in unrighteousness. One is to exchange right for wrong. That’s what the prophet Isaiah condemned when saying, “Woe to those who call evil good, and good evil; who substitute darkness for light and light for darkness” (Isa. 5:20). In our society, for example, virtues such as virginity and fidelity in marriage are branded as old-fashioned and prudish, while promiscuity and adultery are heralded as contemporary and liberating. Social pressures can cause undiscerning or weak Christians to yield to confused and godless moral standards.
Another way to rejoice in unrighteousness is to be undiscerning about what you expose yourself to. The humanistic philosophies and blatant immorality of our society can quickly dull your moral and spiritual senses. Therefore you must carefully evaluate what you read, view, and listen to. Does it denigrate God and exalt violence, crime, immorality, slander, and the like? If so, and you find that book or article entertaining, you are rejoicing in sin.
Some believers actually rejoice over the sins of others. That’s what Jonah did when he refused to preach at Nineveh for fear the people would repent and God would forgive them. He preferred to see them continue in sin rather than reconcile with God. That attitude is not so far removed from today as we’d like to think. I’ve known professing Christians who wanted out of their marriages so badly that they hoped their spouses would commit adultery so they would feel justified in getting a divorce. What a convoluted perspective!
True love cannot rejoice in sin but glories whenever righteousness prevails. If you love God, the things that please Him will please you, and the things that offend Him will offend you. Let that always be your standard.

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If Your Brother Sins Against You
  If your brother sins against you, go and tell him his fault, between you and him alone. If he listens to you, you have gained your brother. But if he does not listen, take one or two others along with you, that every charge may be established by the evidence of two or three witnesses.  If he refuses to listen to them, tell it to the church. And if he refuses to listen even to the church, let him be to you as a Gentile and a tax collector.  Truly, I say to you, whatever you bind on earth shall be bound in heaven, and whatever you loose on earth shall be loosed in heaven.  Again I say to you, if two of you agree on earth about anything they ask, it will be done for them by my Father in heaven.  For where two or three are gathered in my name, there am I among them.”     
 Matthew 18:15–20