The Post-Birthday World — Lionel Shriver

American children's book illustrator Irina McGovern enjoys a secure, settled life in London with her smart, loyal, disciplined partner, Lawrence--until the night she finds herself inexplicably drawn to kissing another man, a passionate, extravagant, top-ranked snooker player. Two competing alternate futures hinge on this single kiss, as Irina's decision--to surrender to temptation or to preserve her seemingly safe partnership with Lawrence--will have momentous consequences for her career, her friendships and familial relationships, and the texture of her daily life.