This is a predicament that many of us single parents face all too often. Unfortunatley, this is a decision that is entirely up to you at this point. But, I would like to offer some advice that is merely my own opinions. Whether your son is eleven or eighteen, his curiosity about is father will not cease until he is able to satisfy his wonders. In other words, your son will most likley search for his father one day with or without your permission or protection. As difficult as it might be I feel that it is very important to be supportive and as understanding as you can be regarding the situation. Even though it sound like this guy is a real jerk, it is very important not to let that message be sent to your son. Try not to degrade your ex in front of your son. Explain to your son that his father was not taught how to properly take care of himself much less any children. If his father played music,played sports, or anything positive, tell your son about these attributes. This may give him something to identify himself with. Also, I feel this experience, if properly handled can enable your son to be an excellent father one day because he will be encouraged to not make the same mistakes. Sometimes experiences like these cause an opposite reaction than one might think. This approach may satisfy his need to interact with his father or it may not. If not, as I mentioned before he will most likely want to find out on his own. This will be hard for you at first, but hang in there. Your son will eventually be able to determine whether his father is worthy of his love and presence. This may or may not be painful for your son, but realize that we cannot protect them from everything all of there life. Be strong!