No, he absolutely should have told her. There is always a risk of transmission even if very small (if he forgets to take the meds, vomits, or there is a manufacturing issue). Not saying the latter is likely but the partner needs to be aware so they can make an informed decision to rely on the medication and the person taking it and risk assessment. This would apply to any lifelong, incurable disease let alone one that carries a stigma. There isn't an excuse.
He put himself first as he is doing now.
OP, I would just let him know that you won't be routinely coming to any more appointments and that's that. It's your turn to put yourself first. He doesn't need you there.
He managed fine for four years and he will manage fine again. I'd be quite cut and dried about this rather than fannying about with counselling you don't want for the purposes of accompanying him.
I have worked in sexual health and it isn't common for HIV patients to bring partners or family in for their routine appointments. It's usually just weight and height, bloods, a history, swabs/urine if required and then the prescription. They know the drill and just get on with it.
Tel him to be well hydrated. That makes venepuncture a lot easier. A chaperone is always available so he won't be alone.
I'm surprised you stayed with him after that too though, tbh.