One of the worst break-ups I’ve ever heard of was in a short story by Ruth Rendell. It begins after the fact, but what happened was, this guy spent a year in Australia while the woman he’d promised to marry stayed in England. He came back, was met by her or went right to her/their apartment, had sex with her and then, over breakfast, told her he was going to marry a woman he’d met in Australia.
SPOILER:
He’d come back to pack up his stuff and send it to Melbourne. Instead, he was packed up and sent to Melbourne.