Objection 1. It would seem that even before the marriage has been consummated one consort cannot enter religion without the other's consent. For the indissolubility of marriage belongs to the sacrament of matrimony, inasmuch, namely, as it signifies the union of Christ with the Church. Now marriage is a true sacrament before its consummation, and after consent has been expressed in words of the present. Therefore it cannot be dissolved by one of them entering religion.
Objection 2. Further, by virtue of the consent expressed in words of the present, the one consort has given power over his body to the other. Therefore the one can forthwith ask for the marriage debt, and the other is bound to pay: and so the one cannot enter religion without the other's consent.
Objection 3. Further, it is said (Matthew 19:6): "What God hath joined together let no man put asunder." But the union which precedes marital intercourse was made by God. Therefore it cannot be dissolved by the will of man.
On the contrary, According to Jerome [Prolog. in Joan.] our Lord called John from his wedding.
I answer that, Before marital intercourse there is only a spiritual bond between husband and wife, but afterwards there is a carnal bond between them. Wherefore, just as after marital intercourse marriage is dissolved by carnal death, so by entering religion the bond which exists before the consummation of the marriage is dissolved, because religious life is a kind of spiritual death, whereby a man dies to the world and lives to God.
Reply to Objection 1. Before consummation marriage signifies the union of Christ with the soul by grace, which is dissolved by a contrary spiritual disposition, namely mortal sin. But after consummation it signifies the union of Christ with the Church, as regards the assumption of human nature into the unity of person, which union is altogether indissoluble.
Reply to Objection 2. Before consummation the body of one consort is not absolutely delivered into the power of the other, but conditionally, provided neither consort meanwhile seek the fruit of a better life. But by marital intercourse the aforesaid delivery is completed, because then each of them enters into bodily possession of the power transferred to him. Wherefore also before consummation they are not bound to pay the marriage debt forthwith after contracting marriage by words of the present, but a space of two months is allowed them for three reasons. First that they may deliberate meanwhile about entering religion; secondly, to prepare what is necessary for the solemnization of the wedding. thirdly, lest the husband think little of a gift he has not longed to possess (cap. Institutum, caus. xxvi, qu. ii).
Reply to Objection 3. The marriage union, before consummation, is indeed perfect as to its primary being, but is not finally perfect as to its second act which is operation. It is like bodily possession and consequently is not altogether indissoluble.
Source: Summa Theologica (New Advent)