[R. Scott]

"He tells me he won't drink as much after we get married." "I know she cheated on me while we were dating but she wouldn't do that if she had a ring on her finger.”

Just like the women who think they can change the man after marriage, or the man who cheats on his wife with a married woman, both get divorced and marry – and then are surprised to find one is cheating again.

[najida]

There are also behaviors that may not come to full bloom until the marriage is underway....

Mild jealousy becomes insane jealousy as the social circle enlarges,
A few drinks when stressed becomes heavy drinking during hard times.
Timid insecurity becomes rabid control freakishness.
etc

Granted, most of the flags are there, but some are folded and in the drawer at the time of marriage.