One Day in December by Josie Silver

On a snowy December day, Laurie is sitting on a crowded London bus when she looks out the window and locks eyes with a stranger waiting at the bus stop. The connection is instant and undeniable, but before either can react, the bus drives away. Convinced he is "the one," Laurie spends a year searching London's pubs and streets for him, supported by her best friend and roommate, Sarah.

Their reunion finally happens at a Christmas party, but with a crushing twist: Sarah enthusiastically introduces her new boyfriend, Jack—who turns out to be the exact man from the bus stop.