A common theme in fics where Thoschei are married is the companion shocked that the Doctor hasn't divorced the Master, and the answer being that they just aren't possible for Time Lords, which ok, I can see where this is coming from, but I deign to disagree.
We are talking about a society where people live thousands of years, so inheritance is either a non-issue or something that can't be resolved in one document. Individuals change drastically every now and then and like even (modern) catholic church recognizes incompatibility of characters as a reason to invalidate a marriage. Private property seems to exist in a semiotic void of British landed gentry having a barn with no livestock in sight. Labor market seems to be monopolized by the state, as is reproduction, though on the other hand taxes and exemptions from those don't seem to be a thing either. Of course there got to be ways of dissolving marriages, in fact a better question would be if marriage would evolve in the first place, but I guess especially with a semi-totalitarian (postmodern nostalgic tropes are immune) state you want to be able to designate your next of kin. This would naturally be an absolute bureaucratic pain in the ass, with checking how the spouses exist in each other's timeflows, possible bigamies with different species, possible bigamies with each other, transcriptions of marriages from different societies, and of course loom applications.
Which is why I think that what actually happened was Thoschei getting done with this bs and instead of going to a civil servant, they breached the barrier to the Under-Universe to summon the pantheon god of interpersonal relationships and went "Can you marry us, pretty please?", so now the thing is kinda inscribed in the fabric of multiversal collective consciousness, and as such somewhat harder to dissolve than a civil contract.
All of which happened mainly because the Doctor learned of this fascinating human idea of "tax benefits".
