Would it be considered a sin in God’s eyes if you were to marry a divorced person if the cause of the divorce was not this person’s fault?
As you are no doubt aware, Jesus gave very definite rules concerning marriage and divorce. He totally disallowed divorce (see Mark 10:11-12).
The law of God allows only one living companion. Only the death of one of the marriage partners can release the other from obligation. Only then is he or she free to enter into another marriage contract.
Jesus stated His standard again in Matt. 5:32 (NIV): “I tell you that anyone who divorces his wife,…causes her to commit adultery, and anyone who marries a woman so diorced commits adultery.” For more on this law follow this hyperlink.
The apostle Paul summarizes the Christian position in Rom. 7:1-3, “Do you not know, brothers—for I am speaking to men who know the law—that the law has authority over a man only as long as he lives? For example, by law a married woman is bound to her husband as long as he is alive, but if her husband dies, she is released from the law of marriage. So then, if she marries another man while her husband is still alive, she is called an adulteress; but if her husband dies, she is released from that law and is not an adulteress, even though she marries another man” (NIV).
You ask if the standard is different for the one who causes the divorce, as opposed to the one who is the victim of it. According to Jesus’ inflexible law, both parties are affected equally, without respect to who initiated the divorce. Of course, if one partner is a committed believer and the other is not, there is a difference in their accountability before God. But since a marriage is binding until the death of one of the partners, even if one does not bring about the divorce the original contract still stands in the sight of God, and neither partner is free to remarry as long as the other partner lives.