Hi S.,
It sounds like you are a little overwhelmed by this whole situation. You say your son's doc diagnosed OCD and prescribed Xanax, but it increased anxiety so you took him back off of it. Without knowing how long he was taking it before you stopped, it is hard to make a judgement, but I do know that drugs that work on brain chemicals can be very dangerous and sometimes need to be slowly weaned off instead of just eliminated. Have you checked with your son's doc since? Does he know you discontinued the prescription?
You also say that your son is seeing a couselor and that is helping some. Is the conselor the doc that prescribed the Xanax?
Honestly, the best advice I can give is for you to get another medical opinion regarding the OCD while continuing with the counseling. If your son really does have OCD, he may be able to cope without medication (as long as counseling continues) or my need to try a different medication.
Counseling is not a quick fix, but you say it is helping so keep with it. Are you also seeing a couselor? I would recommend it for both of you. You have a lot of responsibility being a single mom and a lot of stuff to sort out regarding your ex. Counseling can really help you get to a place of confidence in yourself and your abilities as a parent. You and your son will both benefit.
Be brave! :)