It's crazy how close you can be with some people. You know each other like the back of your hand. You finish each others sentences. You spend every minute you can with each other. When certain songs come on, they were your songs. The songs you two belted out while on the way to the mall or to grab some lunch. You had a common place where you always met and you thought you guys were always meant to be sisters, not best friends.
But then over time, you gain different goals in life. You start down a new, intriguing path and they stay on the same, old path that you two once walked. After awhile your paths may run parallel, but usually not. Yours tends to go in a separate direction due to all the turns and loops, taking you further and further from their path.
You both experience new things, find new friends, and find new common places. When you later think about it, you see how much life has changed. Not only yours, but theirs. You listen to different songs. Your friends don't resemble them at all. You are studying in school and they aren't. You wind up in two totally different places even though at one point you were in the same exact spot.
You lose them. You lose track of them from all the stresses of life and how busy you are. You put in the effort to see each other, but it never works out. And you two are now totally different people and your paths don't cross anymore. Maybe it's for the best, but deep down you still think about them when that one song comes on. They cross your mind, but not your path. But then again, maybe it was destined to be that way after all.