What do you do if a guy breaks up with you by simply never talking to you again and you never get an explanation?

He's lower than pond scum. It's a chicken way out. This guy holds no moral values and doesn't mind hurting those close to him. Consider yourself lucky that you are rid of him. It doesn't matter what his reasons were, but what does matter is he wasn't mature enough to talk to you about why he wanted to break the relationship up. Just let it go.