So what the fuck did Roodaka mean by marriage?
This was like. a Thing in Web of Shadows. Literally Sidorak's primary motivation is he wants that vortussy, but the horny vibes are actually just that: vibes. Despite the general way that Roodaka is, there's no implication of reproduction or physical attraction, not even a chaste peck on the cheek (although let's be real there would be tongue involved). Honestly, bringing in the Romance Isn't Canon sledgehammer isn't even necessary for the vibes to be there that this needs to be more than just for romance.
So what does marriage actually mean to them if it's debatably romantic in the first place? Obviously political marriages happen in humans all the time, even if they're not considered the norm any more, but I'd wager that for societies so heavily structured around industry and profit as Xia and Stelt, I think it actually makes a lot more sense for marriage to have originated as a form of political or business agreement in the first place - a binding of two people and a unison if their assets for further gain for the two of them. It could literally be like merging or buying another company, or bringing someone into a position of power for their acumen in a way that is more solidly enshrined than typical employment. There's probably weird other shit going on because to be honest I'm not entirely clear on what the point of human marriage is either, but there's a lot to chew on while still having it make sense that Roodaka can lead Sidorak around by his dick for the entirety of 2005 if his dick is recontextualised as a profit motive.