It’s funny how quick people just stop caring about you after you stop putting an effort into a friendship. You realize that without your participation, there is absolutely nothing left. That the friendship was only alive because of your constant interest. Therefore, they obviously were neutral about the whole thing. You never mattered to them. You were just another person to have around.
It just hurts because, unlike them, they actually meant something to you. And when you realize this, and start losing everyone one by one, you are completely alone. And that is hard, to go from ignorance and company to knowledge and solitude.