August 27 reading and my commentary

Memorial of Saint Monica

Reading 1, second Letter of Saint Paul to the Thessalonians 3:6-10, 16-18

We instruct you, brothers and sisters,
in the name of our Lord Jesus Christ,
to shun any brother
who walks in a disorderly way

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When I tried to Google this specific reference, I found an awful lot of commentary essentially on the verses that follow this one, about not being idle and finding work, no matter what type of work that is... but I wanted to know specifically about this one -- which to me it seems to be saying:

If you know someone as a Christian, who then walks in a disorderly way, we are to shun them (like the Amish do ??? is this there Scriptural basis for so doing ???)

I guess I have more questions, than commentary -- so this means, for someone I know to be a Christian, I should shun them when --

they have a sexually active relationship outside of marriage ???  does this apply in each and every circumstance this can happen in the life of  a Christian???  what about the lonely ... the fatherless woman with two sons who need a man's hand ... those with deep-seated wounds who have no recognition of that, who don't know they need help, who are lost, who don't hear about this from the pulpit and who aren't ones to read self-help  ... the financially dependent ... the medically dependent (on either side of the equation) ... those whose church forbids any type of remarriage ...