C. S. Lewis:

To love at all is to be vulnerable. Love anything, and your heart will certainly be wrung and possibly be broken. If you want to make sure of keeping it intact, you must give your heart to no one, not even to an animal. Wrap it carefully round with hobbies and little luxuries; avoid all entanglements; lock it up safe in the casket or coffin of your selfishness. But in that casket - safe, dark, motionless, airless - it will change. It will not be broken; it will become unbreakable, impenetrable, irredeemable... The only place outside Heaven where you can be perfectly safe from all the dangers of love... is Hell.