When is it appropriate to sever communication with someone?
In my early 20's I was a member of a particular church group. They recommended I cut ties with friends who were not interested in church, to limit possible negative influences. That was the vast majority of people I knew, including relatives! Today, I understand the aim of that advice, but the approach was fearful, faithless and lacking love.
Nearly 20 years later, it was an obvious mistake to follow the letter of their legalistic suggestion. A meal together every so often, or a phone call (not to only again invite them to church) would have been appropriate. Not associating with someone because they practice certain activities is questionable. If the activity is searching for loose encounters (what a nightclub atmosphere provides, for example), then that activity one can excuse themselves from, without excusing the friendship altogether.
Today, there is a wiser and more loving approach to those who may not agree with the notion of God and His Way. Alienating them or excommunicating them is not loving them.
However, there is a time where this is appropriate and arguably necessary: past intimate relationship(s).
Speaking from experience, continuing to communicate with a well intending past lover is like unlocking a door which time and circumstance can easily open. The rejection isn't rejecting the individual. Whether they are in fact cause for temptation or express moral restraint, the tie being cut is the cause for wickedness to occur. Communication must absolutely cease.
God hates infidelity, it leads to divorce, destroying families and God's good work.
And if your right hand causes you to sin, cut it off and throw it away. It is better for you to lose one part of your body than for your whole body to go into hell.
- Matthew 5: 30