It Ends With Us by Colleen Hoover

It Ends With Us, book 1

paperback 

Lily hasn't always had it easy, but that's never stopped her from working hard for the life she wants. She's come a long way from the small town in Maine where she grew up--she graduated from college, moved to Boston, and started her own business. So when she feels a spark with a gorgeous neurosurgeon named Ryle Kincaid, everything in Lily's life suddenly seems almost too good to be true ... But Ryle's complete aversion to relationships is disturbing. Even as Lily finds herself becoming the exception to his 'no dating' rule, she can't help but wonder what made him that way in the first place