This is the second great quote I've found on Happy Catholic's site this week. This one is by C.S. Lewis:
"To love at all is to be vulnerable… If you want to make sure of keeping your heart 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 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 of Heaven where you can be perfectly safe from love is Hell."