Having read every Discworld novel and without looking it up, that sounds right. As I recall Mistress Weatherwax had been seeing alternate timelines as part of a side effect of the Elve's world intersecting the reality of the Disc, and she's married to Ridcully in some of them, as they apparently were involved in their youth. She does later note to Ridcully that, from what she saw, their alternate selves that had married appeared happy.

In my personal opinion it is one of the worst Discworld books, which still makes it pretty good mind you.