Whether you realize it or not, you are trying to punish your ex by giving him the silent treatment. On the face of it, he is in the wrong as he refuses to discuss matters with you. However, some individuals genuinely do not like conflict and will avoid it at all costs.
Similarly, you may well be overly-sensitive about certain issues, but his refusal to discuss your concerns is only serving to heighten them.
Have you told him how he makes you feel? Have you asked him to help you not feel so upset and stressed out? If he doesn't talk to you, perhaps you could write him a short letter. No more than one side of a page. Don't accuse him or blame him for anything. Simply write down how you are feeling. Tell him that you would appreciate his help and support, especially as he seems to cope so well. Perhaps you could agree to sit down for an hour each week, so that you can both discuss any burning issues that you may have.
Failing this, you should seriously consider visiting a counselor. If your partner doesn't go with you, then go alone. Communication is a vital aspect if any relationship. As it stands, the lines of communication have broken down, and that's where your relationship is heading, if something doesn't change.