Marriage is a life-long commitment and should be pursued with the help and blessing of God, who is the author of all love.
Here is a prayer from A Manual Of Prayers for the Use of the Catholic Laity that can be prayed by someone about to be married.
O gracious Father, who dost bless us by Thy bounty, pardon us by Thy mercy, support and guide us by Thy grace, and govern us by Thy providence: I give Thee humble and hearty thanks for all the mercies which I have received at Thy hands in time past.
And now, since Thou hast called me to the holy estate of marriage, be pleased to be with me in my entering into it and passing through it, that it may not be a state of temptation or sorrow to me by occasion of my sins or infirmities, but of holiness and comfort, of love and dutifulness, as Thou hast intended it to be to all that love and fear Thy holy name. Amen.