Brian,
bmerr here. Situations such as the one you describe are due to the fact that Biblical teaching on marriage, divorce, and re-marriage has been widely neglected by the religious community in general.
The Bible is not silent concerning the issue, however. For example, Jesus said in Matt19:9,
"And I say unto you, Whosoever shall put away his wife, except it be for fornication, and shall marry another, committeth adultery: and whosoever marrieth her which is put away doth commit adultery."
In Matt 5:32, Jesus said,
"But I say unto you, That whosoever shall put away his wife, savinig for the cause of fornication, causeth her to commit adultery: and whosoever shall marry her that is divorced committeth adultery."
Also, in Mark 10:11, 12 we read,
"And he saith unto them, Whosoever shall put away his wife, and marry another, committeth adultery against her. And if a woman shall pur away her husband, and be married to another, she committeth adultery.
We need to realize that it is not the authority of human governments or judges that joins a man and woman. It is God that joins man to wife. To be sure, there are as many different man-made laws concerning marriage as there are human governments. But marriage is God's institution, not man's.
In Matt 19:5, 6, Jesus recalls the beginning, when marriage was instituted, and He said, "What therefore God hath joined together, let not man put asunder."
The only thing that ends a marriage in the eyes of God is infidelety of one of the marriage partners. Even then, divorce is never commanded, but it is permitted. The innocent party then may remarry, the guilty may not.
Due to the fact that God's truth concerning marriage, divorce, and re-marriage has been widely neglected, many people have ptu themselves in a situation where the "marriage" they are now in is actually an adulterous relationship.
I've got to go, but let me draw your attention to Rom 7:2,3.
Also, regarding whether former marriages were before one "got saved", the text says "whosoever". In John 3:16, "whosoever" means anyone. It means the same thing in Matt 19:9.
In Christ,
bmerr