My (recent) ex did this to me (actually was an email) after seeing each other for almost two years. I was taken back that she just didn't have the decency to at least call and tell me. I didn't bother responding to her because I figured that there really isn't a point. I wouldn't try to convince her otherwise as I believe people should be able to make their own decisions. She never hung out with any friends and a week prior she said she was hanging out with "friends." I believe that she met someone and sent the email as not to have a confrontation. Wish I didn't miss her, I think it was kinda messed up to do that.