What do you do when you find a fellow Christian sinning? The world has two answers. The first is to get angry and ostracise them. The second is to support, or even participate in the wrong doing.
As Christians, neither option is morally acceptable. Although a consistent or grave sinner should be cast out of the Church (1 Corinthians 5:1-8; Matthew 18:15-17) in the hope that they repent, the first course of action should be grace. The goal is always restoration, not division.
In his letter to the Galatians, Paul calls this the "law of Christ". We are to gently correct evil, and "bear one another's burdens". The temptation may be to get angry, but who among us can claim to be sinless? A time may come when the roles are reversed. Similarly, our emotional connection to a sinner may cause us to empathise with the sin itself, but all this does is drag us down into the same pit, where we are of no use, either to the sinner or to God. This is why Paul urges us to watch out for ourselves so we may not be tempted.
The solution, therefore, is love. We are to take no pleasure in wrongdoing, but rejoice in the truth. God loves the sinner, and desires their restoration. Thus, we must love the sinner and desire their restoration. We gently point out the fault, and work on a solution. We set aside all personal biases, and pray without ceasing, both together and individually, and a solution will be found far greater than the sin in question.