'Unfaithful' in the Bible

‘As for the person who turns to mediums [who consult the dead] or to spiritists, to play the prostitute after them, I shall set My face against that person and will cut him off from his people [excluding him from the atonement made for them].

And they shall confess their iniquity, and the iniquity of their fathers, through their unfaithfulness wherein they were unfaithful to me, and also that they have walked contrary unto me,