'Unfaithfulness' in the Bible

for they have taken of their daughters for themselves and for their sons, and have mingled the holy seed with the peoples of the lands; and the hand of the princes and rulers has been chief in this unfaithfulness.

Then were assembled to me every one that trembled at the words of the God of Israel, because of the unfaithfulness of those that had been carried away; and I sat overwhelmed until the evening oblation.

And Ezra arose from before the house of God, and went into the chamber of Jehohanan the son of Eliashib; and when he came thither, he ate no bread and drank no water; for he mourned because of the unfaithfulness of them that had been carried away.