It seems more modern, and more like western bullshit for this to happen:
"I love you!"
"Prove it. Swear it. Also, I need a verbal signature in front of witnesses, and jewelry to boot, so everyone else knows too, even when I'm not around."
Me and my helpmate aren't married. We didn't have vows, no ceremony, no tradition. We've been together for fourteen years, would die for each other, and love each other more than ourselves. Why do I call her helpmate, when the government says we're common-law married? Because she helps me. It's more real to me than 'wife', she's not my wife, she's a part of me. The very idea of marriage has been laughable to me since I was young, /especially/ the oaths. Maybe Zalanthas are stupider than I am, but in a world of corruption, betrayal, and murder, I doubt words or ceremonies really mean anything at all.
Despite all that, I've seen and played those who have varied traditions, unique relationship backgrounds, parents of 'one mother, six fathers' or 'one father, many women to breed with, who keeps the children, and the mothers leave'. I've also seen ring giving, or tattoos shared, blood rituals.
Don't box me in with your fifty years or less of experience when Zalanthan culture has had Ages to progress, and they're richer and more cultured and more varied that most of America, imho.
However, if you truly don't find it believable, there's no reason to suspend disbelief. Make a char, with a background that includes a 'marriage' ceremony between their parents, and walk around acting as if everyone else is crazy for not understand this. Call marriage 'ezkontza' and marrying someone 'kontzeko'. That alone should provide an interesting RP experience.