If you are sad and guilty. There’s no harm in saying sorry to your ex. Here, everyone has commented that you did good by dumping him as you were not happy with him. No doubt happiness count but this also bring another question that what about his happiness? His emotions? his faith and his love? He has not done anything bad to you. He still loves you and is good to you. UpTo some limit I see you selfish too. Sorry to say that.
I too was dumped by my girlfriend and I kept chasing and saying her that she mean the world to me and we can talk and fix the things which makes you unhappy and she disconnected all means of communication. I was in deep pain but I continued my usual day to day activity and kept sending her emails as that was only way to reach her. It was very tough for me but I didn’t leave the hope as my love was real. She felt my absence after 3 months and asked can I forgive her and forget everything and start a fresh. I said Yes and now I am father of 2 kids. 🙂