'Unfaithfulness' in the Bible

But they acted treacherously against the God of their fathers and played the prostitute with the gods of the peoples of the land, whom God had destroyed before them.

So all Israel was enrolled by genealogies; and they are written in the Book of the Kings of Israel. And Judah was carried away into exile to Babylon because of their unfaithfulness [to God].

So Saul died for his trespass which he committed against the Lord, for his failure to keep the word of the Lord; and also because he consulted a medium [regarding a spirit of the dead], to inquire of her,