Why won't some people stay in your life?

This one girl that was my friend talked about me and my best friend behind our backs and calling us hurtful names and now she doesn't wanna talk to me anymore. I didn't do anything. She removed me from her Facebook friends list. I was going to ask her but she already removed me. She doesn't have a Facebook anymore. I don't know if she blocked me or deleted her Facebook. She won't speak to me anymore. I'm suprised that her dad is still friends with me on Facebook but he barely talks to me or never asked what was going on. Whatever I don't really care anymore. This girl and I were friends for seven years.
My other friend just stopped talking to me for no reason. When I texted her she stopped responding to me. I asked why isn't she speaking to me or if she is mad at me. No respond. It was like that for 3 months. I gave up for 6 months. I got a new number and new phone. I texted her. She responded "Who is this?" I told her it was me and she didn't respond back. I'm a very nice, kind, loving and caring person. Why would some people stop talking to me? My older sisyer said straight up and bluntly that not everyone I will me will stay in my life forever.