Landline by Rainbow Rowell

Georgie and Neal love each other, there's no doubt about it, but lately it doesn't seem like enough to save their marriage. Two days before they're supposed to leave for Christmas, Georgie tells her husband she can't go because something's come up on her show, and much to her surprise, Neal actually takes the kids and goes home without her. Now she really thinks she's done it. When Georgie finds a way to talk to Neal in the past, she has to face whether or not they would have been better off not married at all.