1. You reciprocate affection in public.
2. You know each other's true motivators in life.
3. Nothing is considered too personal between you.
4. You have adorable nicknames for each other.
5. You protect each other from outside forces.
6. They have a really close relationship with your parents.
7. You can always say exactly what's on your mind.
8. You fight as if you've been doing it for years (because you have).
9. But you know exactly what to do to get them to stop being mad.
10. Ultimately, you spend every waking minute together, so how could you possibly make time for anyone else?
All images courtesy of NBC Universal.