The Other Wife by Jack Finney

The Other Wife by Jack Finney (Saturday Evening Post, January 30th, 1960) starts with a fairly stereotypical husband-wife encounter—she’s prattling on about her knitting and he’s day-dreaming about a sports car—which eventually devolves into a mild spat. During the early stages of this encounter the husband discovers a 1958 Woodrow Wilson coin in his change: this becomes significant later.
The next part of the story sees the husband transported to an alternate world where, after seeing a “Coco-Coola” sign, he notices other changes (the cars are all black, and they are of different makes) before discovering the most significant difference on his arrival back at his apartment—which is that he is married to another woman.
He later realises that she is an ex-girlfriend of his, although this takes some time, and after some slight hesitation he picks up where he left off. He subsequently enjoys a honeymoon period with his other wife and during this also has the pleasure of finding new books that exist in this world but not in his own:

There on the revolving metal racks were the familiar rows of glossy little books, every one of which, judging from the covers, seemed to be about an abnormally well-developed girl. Turning the rack slowly I saw books by William Faulkner, Bernard Glemser, Agatha Christie, and Charles Einstein, which I’d read and liked. Then, down near the bottom of the rack my eye was caught by the words, “By Mark Twain.” The cover showed an old side-wheeler steamboat, and the title was South From Cairo. A reprint fitted out with a new title, I thought, feeling annoyed; and I picked up the book to see just which of Mark Twain’s it really was. I’ve read every book he wrote—Huckleberry Finn at least a dozen times since I discovered it when I was eleven years old.
But the text of this book was new to me. It seemed to be an account, told in the first person by a young man of twenty, of his application for a job on a Mississippi steamboat. And then, from the bottom of a page, a name leaped out at me. “‘Finn, sir,’ I answered the captain,” the text read, “‘but mostly they call me Huckleberry.’”
For a moment I just stood there in the drugstore with my mouth hanging open; then I turned the little book in my hands. On the back cover was a photograph of Mark Twain; the familiar shock of white hair, the mustache, that wise old face. But underneath this the brief familiar account of his life ended with saying that he had died in 1918 in Mill Valley, California. Mark Twain had lived eight years longer in this alternate world, and had written—well, I didn’t yet know how many more books he had written in this wonderful world, but I knew I was going to find out. And my hand was trembling as I walked up to the cashier and gave her two bits for my priceless copy of South From Cairo.  pp. 25-26 (The Year’s Best SF #5, edited by Judith Merril, 1961)

This part of the story, and his realisation about what the odd coins in his change do—see below—is probably the best of it.
In a few months, of course, the shine eventually comes off his new relationship and, while checking his change one night, he finds a Roosevelt coin. He realises that it was the Woodrow Wilson one which transported him to this world—and that the Roosevelt will let him return.
The story ends with him back in his own world where no time has passed. He has a second honeymoon period with his first wife and then, later, finds another Woodrow Wilson coin in his change . . . .
I guess, overall, this story is okay, but it’s essentially shallow New Yorker froth where a bigamous husband has his cake and eats it. A pity, because there is a better story here about how the shine comes off of new relationships and marriages, and of the possibilities of the road not taken. (And hopefully a story which explains the reason there isn’t already a husband in the alternate world.)
** (Average). 5,850 words.