I understand how you feel. It can be a hurtful feeling when your ex can move on and be with someone else. But ask yourself, you were able to be without and perhaps find someone else. Do they not deserve the same thing?
It's a feeling of control that you have lost. I would think that you broke up with him. You had the control and you being the breaker and he I am sure had feelings for sometime. You had a powerful feeling if you were the only one he could care for....This is not true.
There will be a female that he will finally be able to be himself around. Don't sit there and remove him completely. You may need to take time to disconnect for awhile so you can get your emotions in check...which can be vey normal. But if you stil think about him and want to keep contact with him, then do it.
If you are the person who needs to just no longer talk to your ex to get rid of them completely then go ahead. I have ex's I will NEVER speak to again, then again I have a few I still speak too. Because they are a good person and I want them to be happy...but I did need to remove myself from them for awhile to get over the fact they have someone new.