For a marriage to be valid in the Catholic Church, it must be legitimately
manifested by a man and woman who are capable according to law of giving free consent. They must be free of any previous valid marriage.
The Catholic Church recognizes the marriages of non-Catholic Christians as valid and even sacramental. It recognizes the marriages of non-Christians as valid. But for any marriage to be valid, the parties cannot be validly married to anyone else. Civil law does not have the authority to break the bond of a valid marriage for anyone: Catholic, Protestant and non-Christian. “So they are no longer two, but one. What therefore God has joined together, let no man put asunder.” (Matt 19: 6)
The Church allows divorce for the equitable division of possessions, but it considers the persons still married.
A fallen away Catholic who has not officially become a member of another church is still considered a Catholic and cannot validly marry outside the Catholic Church.
Fr. Vincent Serpa, O.P.