It's from the Cher and Nicolas Cage film Moonstruck when Cage's character tries to talk Cher's character into giving into her feelings for him. (She's hesitant, in part, because she's still with his brother!) The quote:
"Loretta, I love you. Not like they told you love is, and I didn't know this either, but love don't make things nice — it ruins everything. It breaks your heart. It makes things a mess. We aren't here to make things perfect. The snowflakes are perfect. The stars are perfect. Not us. Not us! We are here to ruin ourselves and to break our hearts and love the wrong people and die. The storybooks are bullshit. Now I want you to come upstairs with me and get in my bed!"
"We are here to ruin ourselves and to break our hearts and love the wrong people and die." Does it get any better than that? Maybe it does; what's your favorite quote about love?