Q - Why does marriage end once a spouse dies? Why is it not forever?
A - Thanks for the great question! We first have to explain what the Catholic Church teaches about the Sacrament of Matrimony, which we will call marriage.
Ephesians 5: 31-32 says:
"For this reason a man shall leave (his) father and (his) mother and be joined to his wife, and the two shall become one flesh." This is a great mystery, but I speak in reference to Christ and the church.Human marriage is a reflection of the heavenly marriage between Christ and the Church. We can deduce from this that what we have on earth is nothing compared to what we will experience in heaven.
Also, the twofold purpose of marriage is the unity of the spouses and procreation = babies and bonding. Once in heaven these two are no longer needed, because the spouses will be perfectly bound together in Christ and there will be no more procreation. Thus, what marriage points toward - heaven - is found after death and therefore there is no need for marriage to continue forever.
There is also a difference in what happens in Baptism, Confirmation, and Holy Orders. These three Sacraments give an indelible mark or character to the soul. They can only be received once. All the other Sacraments - Eucharist, Reconciliation, Anointing of the Sick, and Matrimony - do not give this mark and thus they can be received again. NOTE: in the case of matrimony it can only be received again by one spouse when the other has died and the bond of marriage has been broken by death.
It is better, therefore, to speak of the lifelong bond of marriage, rather than saying it is forever. As Jesus says, there will be no marriage in heaven between human spouses.
"On that day Sadducees approached him, saying that there is no resurrection They put this question to him, saying, "Teacher, Moses said, 'If a man dies without children, his brother shall marry his wife and raise up descendants for his brother.' Now there were seven brothers among us. The first married and died and, having no descendants, left his wife to his brother. The same happened with the second and the third, through all seven. Finally the woman died. Now at the resurrection, of the seven, whose wife will she be? For they all had been married to her." Jesus said to them in reply, "You are misled because you do not know the scriptures or the power of God. At the resurrection they neither marry nor are given in marriage but are like the angels in heaven." - Matt 22: 23-30I hope this helps.