Your best friend — basically your other half. You know each other's whereabouts about 92 percent of the time, talk more than is necessary throughout the day, and have more inside jokes than could fill up 12 notebooks.
It's a special bond, yours.
Here are a few GIFs that sum it up quite well.
1. You tell each other the truth
2. You have a mutual understanding of your awesomeness
3. When you haven't seen each other in two hours
4. When she's feeling sad you know just what pep talk to give
5. When you discover they hung out with someone else without telling you
6. You both just know (and you remind each other often)