I know of several churches that will withdraw fellowship from a current member who marries into adultery. They do not do so in a spirit of meanness, but rather they do so in order to withhold that person from any possible position of leadership in the church. They are still more than welcome to attend the church, they just have no voting rights within the church. Some people do not like this; they think it too harsh. Others have no qualms with for what they reveal are quite Biblical reasons.
Luke's gospel (16:18) provides a pretty clear answer...
I don't necessarily think that it matters if the sin is a one-time thing or if it continuing, as it is more so the effect of the sin. Consider David in 2 Samuel. When David lusted after, and thereby committed adultery with, Bathsheba, it lead him to indirectly murder Uriah, which led to Nathan the Prophet approaching the King and telling him that his son would die. David admitted to his sin and sought forgiveness. Nathan informed him that God had forgiven his sin, but that the consequence of his sin would follow him all of his days. The sword, violence, would never leave David's house. David's fall began through the sin of adultery. As a result, his house saw discord and violence for years. Would you really want to risk having someone in a position of leadership in your church who is practicing, or has practiced, the same sin that led to continual violence in the house of a man described as being after God's own heart?
Most people seem to think that if God forgives sin He also removes the consequence of that sin, but that is not Biblically true.