This article is from the U.C. Davis FAQ, by David F. Prenatt, Jr. netesq@dcn.davis.ca.us with numerous contributions by others.
Everything will change, and there's no way to predict how things will
change. Even if you and your spouse are the same people before and
after your marriage, the world will treat you differently after you
get married. As a result, you will both begin to see yourselves and
the rest of the world differently and make whatever adjustments are
necessary. One of the most fundamental changes in the way that the
world treats you when you are married is that you are no longer
recognized as an individual. You are treated as one member of a
couple. Most of your friends will also be married couples because the
lifestyles of your single friends will be incompatible with yours, so
your single friends will probably drift away.
 
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