Here’s a short word from Timothy Keller on Christians friendships:
Christian friends are not only to honestly confess their own sins to each other (James 5:16), but they are to lovingly point out their friend’s sins if he or she is blind to them (Romans 15:14). You should give your Christian friends “hunting licenses” to confront you if you are failing to live in line with your commitments (Galatians 6:1). Christian friends are to stir one another up, even provoking one another to get them off dead center (Hebrews 10:24). This isn’t to happen infrequently but should happen at a very concrete level every day (Hebrews 3:13). Christian friends admit wrongs, offer or ask forgiveness (Ephesians 4:32), and take steps to reconcile when on disappoints another (Matthew 5:32; 18:15).