I've been looking through the various sourcebooks, but there doesn't seem to be a human deity who is clearly focused on marriage. My search-fu only turns up various deities who represent various aspects of marriage, but not all that marriage entails ...
Erastil: marriage as a bond which strengthens the community and encourages procreation/the raising of children.
Shelyn: love.
Calistria: sex.
Abadar: marriage as a contract under law (inheritance, etc.).
Asmodeus: similar to Abadar, possibly with a helping of "male dominance over female subservience" on the side.
Falayna (empyreal lady): gives blessings to brides.
Winlas (empyreal lord): religious rituals and ceremonies.
I discounted Lymnieris (empyreal lord), as he seemed more focused on helping people get out of unwanted marriages.
Kofusachi (Dragon Empires): abundance, happiness, and prosperity in marriage. (Not as relevant for my purposes as his worship is centred in Tian Xia, not the Inner Sea region.)
Have I missed anything, obvious or not?
The Golarion gods are independent from each other. They have areas of concern, but they can overlap (unlike for example the old Romans, who had a Goddes of sewers)
What one god accepts as marriage is not marriage in the eyes of another. While Shelyn might consider a simple exchange of vows as marriage, Asmodeus will ask for contracts and long ceremonies.
Different faiths also have different understandings, what marriage is. For Shelyn it´s an expression of love, for Gorum a special bond of arms, for Asmodeus a form of alliance.
ISG describes the different gods views on marriage.