Objection 1. It would seem that the wife may not take another husband, if her husband has entered religion before the consummation of the marriage. For that which is consistent with marriage does not dissolve the marriage tie. Now the marriage tie still remains between those who equally take religious vows. Therefore by the fact that one enters religion, the other is not freed from the marriage tie. But as long as she remains tied to one by marriage, she cannot marry another. Therefore, etc.
Objection 2. Further, after entering religion and before making his profession the husband can return to the world. If then the wife can marry again when her husband enters religion, he also can marry again when he returns to the world: which is absurd.
Objection 3. Further, by a new decree (cap. Non solum, de regular. et transeunt.) a profession, if made before the expiry of a year, is accounted void. Therefore if he return to his wife after making such a profession, she is bound to receive him. Therefore neither by her husband's entry into religion, nor by his taking a vow, does the wife receive the power to marry again.
On the contrary, No one can bind another to those things which belong to perfection. Now continence is of those things that belong to perfection. Therefore a wife is not bound to continence on account of her husband entering religion, and consequently she can marry.
I answer that, Just as bodily death of the husband dissolves the marriage tie in such a way that the wife may marry whom she will, according to the statement of the Apostle (1 Corinthians 7:39); so too after the husband's spiritual death by entering religion, she can marry whom she will.
Reply to Objection 1. When both consorts take a like vow of continence, neither renounces the marriage tie, wherefore it still remains: but when only one takes the vow, then for his own part he renounces the marriage tie, wherefore the other is freed therefrom.
Reply to Objection 2. A person is not accounted dead to the world by entering religion until he makes his profession, and consequently his wife is bound to wait for him until that time.
Reply to Objection 3. We must judge of a profession thus made before the time fixed by law, as of a simple vow. Wherefore just as when the husband has taken a simple vow his wife is not bound to pay him the marriage debt, and yet has not the power to marry again, so is it in this case.
Source: Summa Theologica (New Advent)