This is how life works:
You spend forever acting like you don't care that you're alone, and then someone comes along and fills the void you've been neglecting for so long. Things are great. You think, 'Wow, i'm happy for once.' And as soon as you get used to having them around, they leave. You're alone again. Even more so than before. You tell yourself that you'll never meet someone that's going to take their place. But you will, and you do. And then the process repeats itself.
Over.
And over.
And over.