Ultimately, ADHD treatment is not a personal choice. It affects everyone who must be around it. So, unless someone is willing to end up alone because they chased everyone out of their life, they must respect the feedback they’re getting from those they want to be around.
Has he been given direct feedback about how his behavior makes those around him feel?
Does he understand your past, and how his behavior brings up the pain of it (i.e. feeling super insecure and unsafe)?
I would say the first step is to take stock and make sure your experience is communicated clearly and without any chance of misinterpretation. In the end, you’ll fail if you try to micro-manage his treatment. He will experience it as an attack and a judgement on so many levels. It’s best to explain why you feel the need to do so, and let him decide if he cares enough about you (and the others his behavior affects) to care enough about his treatment.
In the end, you can only control you. You may have to day, “on days when you don’t take your meds, please don’t be around me.” But I would not recommend starting there. Try to have a direct and honest conversation first, provide resources like articles from this site, etc. Try to show him how skipping meds not only affects his quality of life, but the experience of those around him.