When I moved away after college, I left my best friend behind. A best friend that knew everything about me and did most everything with me. Having someone who has such a huge part of your life who you get used to seeing almost every day is the best feeling. To have that suddenly disappear is the worst.
We went from seeing each other every day to maybe once a year. Once a year is barely anything. We still tell each other everything and are constantly texting, but it's just not the same. FaceTime does make it better, but it doesn't really count as seeing each other. Sometimes you just need a hug from your best friend, and when they are an 8-hour drive away that just isn't possible. FaceTime calls don't last as long as you want them to either. Usually after hanging up a FaceTime call, you remember a list of it seems like a million things you forgot to say. When you don't live in the same city, it's much harder to be completely updated on each other's lives.
People are always complaining about romantic long-distance relationships. How hard it is that they don't get to see their significant other. Long-distance friendships are worse. You never get to see your closest friend, and though you have other friends who are closer to you, it's just not the relationship you have with your friend who has known you for years.
When one of you is going through a low point, it's the hardest. You want to just be there for each other. To give a big hug and to sit them down on the couch with some ice cream and watch your favorite movies together. To be able to bring them along and introduce them to all your other friends so you can share the awesome friend you have with the world. When you meet new friends, you tend to imagine how your best friend would fit into this friend group. Who would get along the best, or maybe not get along at all.
When one of you is going through a break-up, the other is just as adamant about wanting to defend the other as if they were there with you, if not even worse. They still want to punch the person who broke your heart in the face, even if they have never met them before. All they care about is that someone hurt you, and they weren't there to help get revenge or to defend you.
Though it is awful being apart for so long, when you do finally get to see your long-distance best friend, it's like nothing has changed. You do everything together the way you used to, and catch up with each other in literally every little detail of each other's lives. Being so far apart only makes the times together again more precious. No matter who you meet, you still love your best friend and you wouldn't have them change for the world. They still will be only a phone call away, and will still help you bury the body, though it may take a few hours for them to get there to help you.