I have someone I used to be friends with that we will call L. L and I met in elementary school and we were practically inseparable from that day on. I was sitting in choir class with them about 2 weeks ago and they sat behind me for the movie we were watching. They randomly just said "I'm not your friend anymore" and stayed quiet the rest of class. When I asked them why they said "I don't wanna talk about it." I asked them today and got the same response and I'm still trying to figure it out.