“To them God has chosen to make known among the Gentiles the glorious riches of this mystery, which is Christ in you, the hope of glory.” Colossians 1:27
Then there is only one reason we must break fellowship with another Christian. That is unconfessed, unrepentant immorality in the other Christian.
“I have written you in my letter not to associate with sexually immoral people.” 1 Corinthians 5:9
For all other Christians it is the other way; we must have fellowship with them. If we do not have fellowship it is because we are not walking in the light. This is not church discipline. This is a natural consequence of sin.