The Midnight Library by Matt Haig

The main character, Nora Seed, finds herself in this library after attempting suicide. She is able to browse the books and see what her life could have been like if she had made different choices. As she explores the different versions of her life, she must ultimately decide which one she wants to live. It's a fiction book that explores the theme of regrets and opportunities, how the choices we make shape our lives and the power of second chances.

“The only way to learn is to live.”

“A person was like a city. You couldn't let a few less desirable parts put you off the whole. There may be bits you don't like, a few dodgy side streets and suburbs, but the good stuff makes it worthwhile.”

“And that sadness is intrinsically part of the fabric of happiness. You can’t have one without the other. Of course, they come in different degrees and quantities. But there is no life where you can be in a state of sheer happiness for ever. And imagining there is just breeds more unhappiness in the life you’re in.”

→ http://www.matthaig.com/books/midnight-library/