I have this theory.

The theory.. that the more important and intimate the emotion between a couple, the fewer the words are required to express it, for instance:

The Stages:

Six words - Will you go out with me?
Five words - I care for you ok?
Four words - You’re important to me.
Three words - I love you.
Two words - Marry Me?

So what’s left? 

The most important and intimate word you can ever say to anybody would be your last stage, stage six. 

 6. One word - Goodbye.