The more important the emotion is, the fewer words required to express it:
Will you go out with me?
I think I like you.
I care for you.
I love you.
Marry me.
Goodbye.

J. Michael (Joe) Straczynski (b. 1954) American screenwriter, producer, author [a/k/a "JMS"]
rec.arts.sf.tv.babylon5.moderated, “A Quote by JMS” (31 Jan 2008)
    (Source)

Straczynski is quoting something he'd previously written on the death of Andreas Katsulas (Feb 2006). A variant of the quote can be found as a sig line at least as far back as Sep 2007:

I had this theory that the more important and intimate the emotion, the fewer words are required to express it.

First it's in dating: "Will you go out with me?" Six words.
"Honey, I care for you." Five words.
"You matter to me." Four words.
"I love you." Three words.
"Marry me." Two words.

But what's left? What's the one most important and intimate word you can ever say to somebody?

It's "goodbye."