''And in another place: the wife is bound by the law as long as her husband lives; but if her husband be dead, she is at liberty to be married to whom she will; only in the Lord. 1 Corinthians 7:39 The apostle has thus cut away every plea and has clearly declared that, if a woman marries again while her husband is living, she is an adulteress.
You must not speak to me of the violence of a ravisher, a mother's pleading, a father's bidding, the influence of relatives, the insolence and the intrigues of servants, household losses. A husband may be an adulterer or a sodomite, he may be stained with every crime and may have been left by his wife because of his sins; yet he is still her husband and, so long as he lives, she may not marry another. The apostle does not promulgate this decree on his own authority but on that of Christ who speaks in him. ''
1 Corinthians 7:15
But if the unbeliever depart, let him depart. For a brother or sister is not under servitude in such cases. But God hath called us in peace.
And it hath been said, whosoever shall put away his wife, let him give her a bill of divorce. 
But I say to you, that whosoever shall put away his wife, excepting for the cause of fornication, maketh her to commit adultery: and he that shall marry her that is put away, committeth adultery.
And I say to you, that whosoever shall put away his wife, except it be for fornication, and shall marry another, committeth adultery: and he that shall marry her that is put away, committeth adultery.
The following is often brought up as evidence that annulments are not allowed:
Therefore now they are not two, but one flesh. What therefore God hath joined together, let no man put asunder.
We must remember that the Pope is not a man, but the Vicar of Christ on Earth:
Amen I say to you, whatsoever you shall bind upon earth, shall be bound also in heaven; and whatsoever you shall loose upon earth, shall be loosed also in heaven.