1. You spend every minute together

When you grow up next door to your best friends, you really do spend every second of your life together. We were literally inseparable. My neighbors were three girls all around the same age as me, so we hardly ever left each other's sides. So many people would get us confused for biological sisters, based on how often we would be with one another. Almost all of my childhood memories included them, from our intense backyard soccer games, "High School Musical" movie marathons, putting on plays for our parents in the basement and hundreds of sleepovers; growing up simply would not have been the same without them.

2. They have known you through every stage of your life

They have seen you through all your life stages: from starting kindergarten, to the awkward middle school phase, to graduating high school--all done together. You were together when you got your college acceptance letters, made the soccer team and when you got grounded in high school for taking your parents car. We have seen it and lived through it all together, which is part of what makes us so close. There aren't that many people you can say you have known basically your whole life. You know almost everything about each other's lives, because you were there to share the experiences.

3. You have two houses instead of just one

You end up acting like their house is your own. My parents would buy food just for my neighbors, and, at times, would end up getting mad at them as if they were their own kids. We share almost everything: our closets would be combined and we'd always have piles of clothes at each other's houses. Whenever you didn't want to be at your own house, you always had a place to go. You can walk into the other's house and be at home, because--let's face it--you were.

4. They turn into your actual sisters

After spending your entire life with people, they become like your actual family. You end up going with them to family dinners, family vacations and college graduations. You know each other's aunts, uncles and cousins as if they were your own. They know exactly how to annoy you, and you will fight like siblings. But you love them more than anything and don't know what you would do without them.

5. You will always be best friends

The best thing that happens when you live next door to your best friends is how incredibly close you get. Now, one of us is 23 years old and the other is 20; we all went in separate directions after high school. But you know nothing could ever change your friendship. Yeah, it sucks when they decide to move half way across the country to go to college, but even though we can't see or talk to each other every day, nothing has changed. Nothing will ever change the last 16 years of memories, and I know it will be the same way for the next 100 years.