Matthew 5:32
But I say to you, every person who divorces his wife makes her become sexually unfaithful to him [i.e., since she will probably marry someone else], unless the reason for the divorce is that she had [already] become sexually unfaithful to him. And whoever marries a woman who has been divorced commits sexual sin with her [i.e., because she is still rightfully married to her first husband].
Mark 10:11
And He said to them, "Whoever divorces his wife and marries another [woman] commits sexual unfaithfulness [toward her].
1 Corinthians 7:15
Yet if the unbelieving mate separates [from his spouse], let him go. The brother or sister is not obligated [to continue the marriage] under such circumstances. For God has called you [believers] to live in peace.