We cannot run away from unbelievers because we would encounter them virtually everywhere we get to. (1 Corinthians 5:10).
We have unbelievers as our colleagues at work, like our relatives, roommates, and teachers. We have not been called to be isolated from the world but to be insulated from it; and this is what God does for us by the truth of the Gospel.
The Gospel already establishes the fact that we cannot have unbelievers as our best friends because there is no basis of fellowship between righteousness and unrighteousness (2 Corinthians 6:14).
Paul, however, admonished us to “walk in wisdom towards them that are without [that is, unbelievers]. We must relate with them in in love. We must also keep in mind that great admonition to “love our neighbor [who may be an unbeliever] as ourselves”.
This biblical wisdom in relating with unbelievers would create a platform to share Christ with them, when the opportunity presents itself.