Mine to Five by Tara September

‘Tis the season for an office romance!
Working beyond nine to five and barely getting by, Melanie Thomas is eager to celebrate the impending holiday season and to toast the start of her dream marketing job over drinks with her boyfriend. Unfortunately, he has different plans—like seeing other women.
Indulging in a pity party with tequila, Melanie confides in a sexy stranger at the bar. It’s almost Christmas, one night of letting go won’t hurt anything, right? Turns out it just might—when the stranger is her new boss. Determined to succeed at her job, Melanie won’t be scared away. This is her chance, even if her hot boss has her feeling all merry and bright and wishing for a less than professional relationship.
Matthew Ryans is burned out and on thin ice at the company he helped build unless he gets his head back in the game. Yet, his head, both upper and lower, are quickly becoming obsessed with his new assistant. Still, he can’t seem to fully begrudge Melanie’s distracting presence and the Christmas joy she brings with it. Especially considering that her enthusiasm has him reenergized. For once, he is longing for Mondays, but with his heart and job on the line he can’t risk blurring the lines no matter how strong the lure of holiday mistletoe is.
Will their holiday passion be able to fuel mutual career success, or will it only get in their way in the New Year?