Just try to hold dry sand with both of your hands and try pressing as much as you can. The more you will press, the more sand will fall from your hands. This is what exactly happening with you. Your ex is just like that sand, which you are trying your best to hold, but the more you try, the more you loose. You are not only loosing him more, but at the same time you are loosing your self esteem also. People who go away from your life, were actually not yours. They had a part to play in your life and their role gets over as they go away. Really believe me, no use of running after shadows. You will never be able to catch them. The more you will try to bring "The Past" back in your life, the more you will be damaging the Present and the future. Also remember one thing, the mirror in which you must be seeing your face daily, if it gets break once, can never be rectified. The crack will always remain how much you try to fill the gap.
So, just move on in life. I am sure the future will have something very good for you and is waiting for you to come and grab the happiness.