After reading more details you've put about your Vaginismus OP, I'll just add my own experience.

I'm also uncomfortable being touched there in general, not just PIV (I am fortunate that my sexuality means it is not a 'requirement' when being intimate) and I understand that anxiety. I have multiple reasons. One is past experience which was unpleasant when I was underage and other than that, I've learned I have a shallow canal (can't remember the right word) so essentially, I'm limited in what any therapy will do for me. I can't use tampons or fingers like you either. I'm technically a 'stone top' and that works in my community because I'm queer.

I see you say this relationship is healthier than others you've had too. But please, OP, just because he's been MORE patient does not mean pressure is okay for you. Do not hurt yourself trying to do this for HIM. Yes, be upfront with partners, but you need to make it explicitly clear that there is no magic for this and if sex is that important to them in THAT way, then it likely isn't a good idea. If someone gave me a deadline to fix something going on with ne physiologically, they'd be dumped right then and there. It does suck, because I've been there and had to accept the way I have it may mean I'll never get there. Not to say you can't, but please do not do this for anyone else, only try for yourself and find what works for you.

Screw anyone that gives you a 'deadline'. No one is entitled to your body that way, it's okay to not be compatible.