There is a lot here and the fact that there has been abuse and boundary issues leads me to think this may be more of a legal issue than psychological. The reason I am stating this is that the only legal thing has been the divorce decree. It may be time to get the opinion of a divorce attorney because the lack of having legal counsel during the divorce process means that you may have agreed to something then that seemed okay at the moment, but not okay in the long run. I would think that the “no-contact” drop-off arrangement is a good place to begin your discussion with a qualified attorney.
The fact that you fear for your son’s safety is of utmost importance. As we wrestle with Coronavirus disease (COVID-19) the poor hygiene, lack of attention to necessary cancer medication and risk of infections means that your son’s safety is at risk. The fact that your ex-girlfriend has a drug habit and is living with your ex-husband while still married with three of her own children makes her statement that your son is ‘her responsibility’ not your’s deeply troubling. You need to take every measure you can to protect your son — and the best way to do this is by getting a legal opinion.
I believe this will also be the most direct way to help your anxiety. More often than not anxiety peaks when we feel we do not have control in a situation. By examining your best options legally you are taking control of what you can in the circumstance. This will give you focus and a good idea of what you can expect going forward. Your son needs you to do what you can do to protect him.
Wishing you patience and peace,
Proof Positive Blog @ PsychCentral