Bond. Something that binds, ties, or fastens things, even people, together. Whenever the people we know a lot or people we're close to changes, we can still feel a faint connection between them. And no matter how hard we try to severe that bond, it will only increase the pain in folds. It's because even if they change, and even if you do too, there's always the past. The past where you were close and have that strong tight bond between the two of you. That past will haunt you forever. And maybe, as the quote says;
“You know how the bonds are, they cling as tightly as vines. And sometimes, like vines, they cling tightly enough to kill.”
It's true, if you think about it. Unconsciously, you get attached to a person and then they will treat your life as if it's a door to walk in and out, and when they do, you will suffer because of their memories, the feelings, etc. You will suffer whether inside or outside, or both as if you're dying and the worse part is you're not. You'll live with the pain.