Why?

Why do people do stupid things? My good friend just got broken up with for no reason! It makes me so mad because I hate seeing him so sad! She said she was ready to marry him and they had a ring all picked out and her parents were all for the marriage, but then she completely flipped and changed her mind and broke up with him. He would have done anything for her and he treated her like a queen. I don't get what she was thinking. I just wish I could understand so I could help him. It is when things like this happen that I realize how important it is to communicate and love someone enough to tell them when you are scared and just how you feel. anyways, I was just frustrated with how she broke up with him, and I know it isn't me, but I am hurting for him! I just want him to be happy.