I don't necessarily imagine that the marriage would have to be abusive not to be a long-term success. I'd be happy with a growing apart fic, or a giant row, or even a separating and eventually getting back together on other terms. But there's NOTHING! Actually, though I don't care for Gregor/Miles, I quite like the idea of Ekaterin/Ivan in one of the fic series on AO3 in that it's a possible different pattern of a relationship for Ekaterin that has quite a lot going for it.