While browsing for a resource on family devotions I came across these prayers for couples, and this one, I liked:
A Prayer for a Couple About to Marry
“O God of Abraham, God of Isaac, God of Jacob, bless these Your servants.
Sow the seed of eternal life in their hearts,
so that whatever they learn in Your Holy Word they will profit from it,
and bring their learning to fulfillment by their deeds.
Look, O Lord, mercifully on them from heaven. Bless this couple.
As You sent Your blessing on Abraham and Sarah to their great comfort,
so send Your blessing on these Your servants.
Help them to obey Your will and always live in safety under Your protection.
May this pair live in Your love to the end of their days.
Through Jesus Christ our Lord, we pray. Amen.”