I also have PTSD from childhood that only recently got a diagnosis. It's really, really tough, because things absolutely get way worse before they get better. You've had all these unhealthy coping mechanisms in place your whole life, and they need to get torn down first before you can start rebuilding healthy ones. It sucks.

It also sucks for our partners, and it sounds like you really understand that. It's so hard to be the partner of someone with PTSD, because they feel like they have to walk on eggshells to avoid triggering you and they have to see you in an enormous amount of pain regularly without any ability to help.

Most people can't cope with being in a relationship with someone with PTSD. That's fine. If someone is going to be in a healthy relationship with someone with PTSD, they need patience, the ability to assert and maintain strong boundaries (eg "this is your pain and not mine", "this is not my responsibility to fix", etc.), and fantastic communication skills.

It doesn't sound like your fiance has any of those. It sounds like he's built up a lot of resentment for how much energy and effort it takes to be in this relationship. I don't know his side of the story, but it really does sound like you're doing everything you should be doing, PTSD-wise. So, maybe you guys are just fundamentally mismatched, which sucks. His frustration and impatience are totally valid, but also really getting in the way of a healthy relationship. You can try re-asserting the importance of couple's therapy, because I think it would be enormously beneficial, but only if he's actually invested in his side - the learning and changing and growing he'd need to do to be in a healthy relationship with you. He may hold too much resentment already (and may just be fundamentally not a person who can handle that kind of relationship). There are people out there who can handle being in that type of relationship. I found one! (I may have taken the only one, technically, but there are probably more.) Good luck.