For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh. So they are no longer two, but one flesh. And, of course, if the new relationship were a true marriage, the intimacy pertaining to it would be marital. So, by saying that such intimacy is not marital but adulterous, Jesus made it clear that a new relationship cannot be a true marriage. Therefore, separating what God has joined is not merely wrong but impossible.
Marriage is indissoluble.
Such cases can be examined by the Church and, if invalidity is established, the marriage is declared null. In such cases, the Church understands Christ's teaching as permitting, under certain conditions, the dissolution of a non-consummated marriage. Christian churches and ecclesial communities separated from the Catholic Church hold, on various grounds, that even the valid and consummated marriage of two baptized Christians can be dissolved. Through the centuries, most Catholic married couples, empowered and assisted by the grace of their sacrament, have resisted temptations, overcome failings and persevered until death in their one-flesh communion. Unfortunately, however, non-belief pervades contemporary culture and in many ways influences our ideas and expectations, with the bad result that many of us bishops, priests, religious and laity now assume that we have a right to personal happiness in this world.