The Bible is very clear on this subject. First, we should always attempt to restore the person. "Brethren, if a man be overtaken in a fault, ye which are spiritual, restore such an one in the spirit of meekness; considering thyself, lest thou also be tempted" (Gal. 6:1 KJV).
If he or she refuses to change, or repent from sin, then you must be careful not to become complacent towards his or her sin. That's why the Bible says, "considering thyself." The word considering means "to watch yourself." If you spend time with a person who is actively living in sin, you will be tempted to commit the same sin.
When the person refuses to be restored, then the Bible clearly indicates your next step.
I wrote unto you in an epistle not to company (fellowship or spend time with) with fornicators: Yet not altogether with the fornicators of this world, or with the covetous, or extortioners, or with idolaters; for then must ye needs go out of the world. But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolater, or a railer, or a drunkard, or an extortioner; with such an one no not to eat.If a fellow Christian is living a lifestyle of sin, we are told not to spend time with them. The main reason for this is to protect us from the same temptation. Remember, we are to love all people, yet there are some with whom we cannot continue a relationship.
(1 Cor. 5:9-11 KJV)
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