I work in HIV care and I think you are feeling quite reasonable about this. Having a partner who is living with a long term condition can be difficult. It's an extra layer of worry and responsibility, never mind on top of it, that in your case, there was dishonesty in your early relationship that this all brings up again.
I think it's perfectly okay to not want to go to his clinic appointments with him. I would say nowadays it would be quite unusual for a partner to attend for a routine appointment, except maybe in the quite early days after diagnosis, if they needed some support themselves or in understanding U=U and viral suppression or around TTC, pregnancy, etc. I have a long-term condition (not HIV, but one I have to take daily meds for and for life) and honestly, even really early on pre-diagnosis, when they actually thought it might be cancer, I've never brought my partner along. It's my responsibility to manage my health. It's not nice to go to the hospital or go for tests, etc. but it's just life when you have a condition that needs lifelong care.
I would expect dh to support me in lots of ways - like taking over at home on a day I feel ill, bringing me whatever if I had to be in hospital for any reason, being understanding that I can't eat or drink certain things, making sure I have the time I need to take care of myself and stay well - like time for exercise and other self care. But he's not my parent. He doesn't need to chaperone me. I could ask and he could offer, but ultimately, it's not his responsibility to attend my appts as long as I have capacity to make medical decisions for myself.
I think it's okay to say no to attending and I think it's okay to offer to support in other ways, but your dh needs to accept his own diagnosis and take on the full responsibility for managing it and handling his own emotions about it. If you are concerned that he may stop taking his meds to manipulate you, then you shouldn't be having sex with him, certainly not unprotected, if you don't feel confident that he is treatment adherent.
That said, one reason you may want to attend with him is to talk to his HCP about your concerns and ask if there is any support for the two of you as a couple. If he is struggling, there is often an in-house psychologist or a peer supporter who he can be referred to for extra support.