Christians are ANYONE who believes that Jesus Christ died on the cross and rose from the dead three days later...and in doing so replaced the old law & defeated death & sin. In believing this, we are washed clean (saved) of sin when asking for forgiveness. We claim him as our Lord & our Savior.
Catholics believe this. So do Baptist, Methodist, Lutherans, Pentecostals, and many other denominations. All are Christians.
Not only that, but the major Protestant religions either derived from Lutheran's (Martin Luther), the Church of England (King Henry, Calvan, & Reformist), or some other reformer of the Catholic Church. The differences are in the interpretation of the laws. The Church of England came about because King Henry wanted to get rid of Queen Catherine and play run around the bed with Anne Bolin. Catherine refused to grant a divorce-King Henry could not force her to give him one under church law. So, he formed his own church. His descendants (including King James-yeah, the King James Bible) followed this new religion. Martin Luther oppossed the extravagance & what he saw (and preached) as the hypocrisy of the Catholic Church (and Priest-who at that time were allowed to marry, hold property, & many times took mistresses). Both of these men (along with others & the after effects of the Inquisition) caused radical reform in the Catholic church (including Priest no longer being allowed to marry, hold property, and leading chaste lives).
As for divorce, infedelity (the one being cheated on's right to have & not the one who cheated), a non-believing spouse's choice to leave (the believing spouse is not held guilty of adultry if marry, again) are the only two instances of church sanctioned divorces/annulments. Annulments can be given if no children were born/adopted during the marriage.