• In fiction:

In George Orwell's Nineteen Eighty-Four, the character Julia expresses her feelings for Winston by secretly handing him a piece of small paper containing just the words "I love you". Within the dystopian world of Nineteen Eighty-Four where sexual love between Party members is strictly forbidden, this was one of the few possible ways this could have been communicated.
The phrase "I love you" is used in The Empire Strikes Back, the fifth installment in the Star Wars series of science fiction films. Before being frozen in carbonite, Princess Leia (played by Carrie Fisher) expresses her feelings for Han Solo (played by Harrison Ford) with an abrupt "I love you". Contrary to the common and mutual response, Han responds with a roguish "I know" as he is placed into the freezing chamber. (This line was actually an improvisation by Ford.) This instance was used again in The Return of the Jedi as Han shows his affection for Leia; the roles are reversed but the dialogue remains the same.