What is the basis for the Catholic belief that a marriage ceases when one of the spouses dies?
The two forms of the Catholic vows of marriage end with: “until death to us part” and “I will love you and honor you all the days of my life.”
There is nothing said about eternity. All of the sacraments are fulfilled when we are united to God for all eternity. The fulfillment of the sacrament of matrimony is the union with God for which it has prepared the husband and wife. This fulfillment does not cause a separation between the husband and wife; they become more united than they ever could have been on earth. It’s just that they are united with everyone who has become united to God in this way with a joy that is completely beyond anything we can imagine.
When considering heaven, we need to think outside of the box of our human experience here on earth. Heaven is all about God. Actually, our life here on earth is all about God also. But we don’t think in this way nearly enough.