That is a crappy feeling, but I've found for me it helps to just be "receptive" to what the universe puts in my path instead of trying to put people or things in my path. Obviously I don't know everything or what will work for you, but hopefully that makes sense. Sometimes people you forgot about pop back up and before you know it, the other people are off doing their own thing. I feel like life comes in "cycles" and some times people aren't meant to be permanent fixtures in our lives. It's like "making room" for new people by "removing" old people in my mind. It just seems like people are really good at removing themselves at inopportune times, but then again, time is pretty much irrelevant in the grand scheme of things, just another illusion of "control" us humans try to put on the world. We will never control existence, just our own existence.