In my campaign a PC showed affection to an NPC and it blossomed. Eventually they were wed and they continued to adventure til it was determined that the npc was with child. Then the PC left her at home to keep her safe.
He uses sending once in awhile to communicate with said wife. And it definitely adds to the roleplaying aspects.
He gave the npc a magical ring as a wedding band, she doesn't have anything that she gave him. So it was pretty much all roleplaying stuff.
This doesn't give the PC any advantages, and if the enemies know about her, it's a disadvantage. She does know how to fight (ranger), so she can kinda protect herself.
It really depends on the characters, some can handle the situation and some prefer to be a galvanizing swashbuckler conan type person.
The true ritual thing is from relics and rituals (scarred lands). It gives the wedded ones luck bonuses or love bonuses or somethin to attacks, saves, and AC when either is in trouble I think. I'll have to read it again. It would be interesting for the PCs to marry each other. It'll never happen in my campaign, the party is a 7 foot tall cat with four arms and horns (knuk), a slutty halfling bard, a "not much role playing" greatsword fighter, and a cleric with not much personality
Marriage imc involves a ceremony, usually religious, with no game effects. Few pcs get married, but it has happened; sometimes it's political (King Malford, a pc, married Queen Moira; he's a gnome and she's a halfelf, their kids are 'gelflings').