So I thought this was an episode of Modern Love on Amazon Prime but I now can't find it.
A man is in a town (on business) and sees a female author doing a book signing in a book store. He realises its someone he had a brief relationship with years ago, so goes to introduce himself.
They spend the night together chatting and reminiscing, and it turns out both are in unhappy marriages. The woman is hurt he never wrote to her when she moved abroad, but he then admits he put her address into a book and then lost the book.
The night ends with them I think just walking and chatting, and both return to their normal lives. The woman reconnects with her husband, but the man decides to end his marriage.
I'd say I watched it about 3 years ago, please help me, it's driving me mad I can't find out what it was!