Something had to have happen. Maybe you said something to someone and they turned around and made it worse. It happens, but the above advice are good. Don't take too much time. If you did say something wrong don't lie about it but apologies for it.
That's a good question. I to had a best friend stop talking to me. I knew her for 20 years we used to do practically everything together. She was there when I had my son and I was there when she had her son. But one day she just stop talking to me know fight know nothing. This happened about a year ago. I was hurt at first then angry then I tried to reach out to her I called left a message she never called me back so I sent a letter I wanted to resolve what ever it was because her son I called my nephew and my son is like her nephew and I didn't want things to be awkward. But she didn't answer that either. I knew this may not be to much help and I know it hurts but you just half to let it go. When she's or he is ready they will find you and if the friendship is meant to be it will. Just try and be patient. There is a saying all good things come to those who wait. Good luck!
Oh this happens to me all the time with this one friend. ( rught now as a matter of fact) Give it a few days, then call or text, talk about what you did wrong if anything. Sometime people do want to be left alone and just find any reason to get upset. But if your friendship is a strong one, this should blow over after a good talk.( our longest fight was 2 1/2 months) I know how you feel, keep busy, good luck