One Day in December by Josie Silver

On a snowy December night in London, Laurie James looks out the window of her bus and sees him-- the man she's convinced, in that split second, is the one. Their eyes meet, he makes a move in her direction... and then the bus drives away. Laurie becomes obsessed, spending months scanning every face at every bus stop and every cafe in the hopes that it's him. But it never is.

That is, until her best friend and roommate, Sarah, introduces him to Laurie at a Christmas party a year later as Jack, the man of Sarah's dreams.

One Day in December is a tense but moving romance spanning almost a decade as Laurie and Jack try to navigate life with each other... but not with each other. Theirs is not the only love story, though. The relationship between Laurie and Sarah is just as, if not more, important than whatever Laurie and Jack may or may not have. It's why Laurie keeps Jack's identity as "bus boy" a secret, so as not to break Sarah's heart. And it's why the ultimate climax of the book takes on an even deeper meaning-- Laurie and Sarah's relationship has to be solid before any relationship between Laurie and Jack can begin.