If you own a home and then get married does your spouse then own half of it?

If your name is the only name on the deed, then no. It depends upon the state in which you reside. Generally property obtained before a marriage is considered solely owned by the deed holder if the new spouse is not added to the property title. However, in some CP states spouses have been successful in gaining property rights even when they were not a title holder or privy to the purchase of said property of the "owner spouse" before the marriage.