Priests, Nuns, and Monks cannot be married in the Roman Catholic Church because their vocation asks them to give their lives totally to the Church and God (although not a title espoused directly by the Church "Married to the Church" is a common term). This is a discipline (as far as Priest's are concerned) and could be removed by the Pope as it is in the Eastern Catholic Churches.
Celibacy has its basis in part from St. Paul in his letter to the Corinthians:
"The unmarried man is anxious about the things of the Lord, how to please the Lord. But the married man is anxious about worldly things, how to please his wife"
The Catholic Church has always valued celibacy in her priests. The very first priests and Bishops - the apostles - were all celibate. We believe that St. Peter was a widower, and, of course, St. Paul was very vocal about his celibacy requesting that all should be like him. Early councils in the first three centuries kept making various rules calling for perpetual celibacy of the clergy. In the Latin Rite, celibacy was enforced by the middle of the first millennium, not always successfully.
Orthodox priests could marry, Catholic priests could not.
Whether or not purgatory existed.
as far as i know they share everything with the roman catholic church except priests can marry and the pope is not the head of there church
Catholicism traditionally prohibits its priests from marrying, as part of the vow of celibacy.
Catholic priests will refuse to marry anyone not belonging to their faith. A Protestant pastor will do the job.
The Vow of celibacy is meant to help priests focus on a relationship with God, rather than a relationship with a partner; Catholic priests are an alter Christus - another Christ, they are to mirror Him in their lives, they are His representatives; they are already "married" to the Church.
Episcopal priests are allowed to marry; I have no problem with that. Perhaps the Catholic Church could allow some priests to marry--I'm not convinced that it is a bad thing. I don't make these decisions, however.
PRIESTS CAN MARRY AND HAVE A FAMILY AND A HOME
In the Roman Catholic Church, it is required that a priest be celibate. This is to keep the priest from being distracted from doing God's will as a priest. However, if an Anglican or Orthodox priest who is married converts to Catholicism he is able to become a Catholic priest and keep his wife. In the Eastern Catholic Church though, the priests are allowed to marry though. Lutheran and Episcopalian Priests are allowed to marry as well.
There can be no such person as a "wife of the Pope". The Pope must be a Cardinal of the Catholic Church. Cardinals are, for the most part Bishops (with a few priests). All priests and bishops of the Catholic church take a vow of celibacy when they are first ordained and cannot ever marry. Even in the Eastern Rites which allow married priests, the Bishops are only chosen from the celibate priests.
Then as now Catholic Priests could not marry; but Anglican Priests who were not members of religious orders were allowed to get married.
Priests do not marry at any age.