How can I forget about him?

Your ex friend didn't mess up anything, blame the guy for his reaction to it. Sounds as though you are obsesses especially if you have known him for 5 years. You say he talks to you now, but obviously doesn't consider you as a future girlfriend. If its affecting you like this, the only thing you can do is make the first move. If you get a negative response from him you are going to have to forget him and move on.