I hadn't heard you mention anything about him in a week or so and I was hoping things had gotten better. You know you are not a horrible mom, so please stop that negative thinking. Things are just out of control, but it's not your fault.
Your son is bipolar and he hasn't be taking his medication for some time. As far as his father thinking that he is taking his medication because because his grades are good, aren't a lot of bipolar patients very creative when they are off their medication?
You have done everything you can do for your son. Your ex has custody, he is the responsible parent. I know this is much easier said than done, but I think you do need to take some time off for yourself. I think you need to pray a lot for your son and ask others to pray for him. You know we are praying for both of you, rely on us. I strongly recommend that you go to some Al-Anon meetings. I know your son is not an alcoholic, but these meetings would help you so much. Most areas even have meetings for parents. Regardless, I think Al-Anon meetings would help you. Go every day if you have to. Find a meeting tomorrow, not an AA meeting, but Al-Anon.
Shy, when my oldest daughter was in high school, we did an intervention for alcohol and put her in treatment. Before we totally figured out what for sure what was going on and what we needed to do, I was going out of my mind, thinking I was going to lose her. We did the intervention when she was 17 while we still could. It took a second trip back to treatment at her request when she was 19, but now she is a very successful young lady with a beautiful little girl.
I feel your pain.
Love and prayers,