Most Helpful Guy
Maybe he found out about something you have done?
I guess you could say something like "I don't know what I have done to hurt you because you haven't told me, but I am sorry".
Don't expect a reply though.
Most Helpful Girl
If you broke up with him, how did he leave you to think that you were still dating? That makes no sense. And what is it you feel the need to apologize for? That you broke up with him? People cannot give you advice if you don't explain the situation in a way people can understand what's going on...