Should I talk to him about some of his issues in hopes that it will make him work on his traumas? Not sure what to do... I don't really want to stop being supportive, but I definitely don't want to cater to his fears, either. :/
Most people who are not trained in how to handle PTSD, or don't have PTSD themselves - they don't realize that it is actually a disservice to the PTSD sufferer to react and bend to every fear.
The more you can hold boundaries with him, the better it will be over the long haul. Things will get worse at first, but this is how healing with PTSD works.
The worst thing you could do for him is to spend more time figuring out how to scream "I love you" at him. Think of it like this - it's like giving a someone addicted to cocaine more cocaine to numb out the pain of the past instead of letting them hit their own rock bottom and finally stop trying to resolve the pain through drugs or through a new relationship or through other things.
You keep focusing on what you can do, and I can see how much you want this to work and want the best for him. The more you try to adjust to all his fears to this extreme level, the more you pull him away from his work to heal. In the end, you can never ever provide him enough love or security to heal the past trauma. Never. You can't.
Your job at this time is to love him enough to tell him no, to love him enough to tell him enough is enough.
The very best thing that friends and partners did for me was to be safe but tell me no when I wanted them to reassure me a gazillion times that they were safe. This kind of behavior (asking for endless proof that someone is safe) has been shown in studies to actually increase anxiety and fears. The reason why most trauma therapies work is because people face the past, and their fears, with some safety with the therapist, and they stop avoiding the past by trying to make new relationships safe and new relationships to fix the pain of the past.
As long as you are there ready to try and reassure him so much, he will keep using that instead of working on it more deeply in treatment. It's way easier than treatment, but he will also never heal as much as he could.
I tell most supporters to get their own therapy and grow, not reduce, their support networks for themselves. I highly recommend this for you as well. It is not because you have done something wrong, but because loving someone with PTSD is hard and takes lots of high level skills.
If he wants to do couples therapy, then let him and his therapist find the couples therapist (if you are ok with that.) It's important that the couole's therpaist coordinates well with his therapist. However, I don't think this should be your primary focus. Individual support for you is critical.
I know you want to tell us that no he is really different when he isn't triggered and he isn't being abusive to you and etc. You are communicating to a group of people that includes other supporters and many sufferers - including many of us who have survived abusive relationships. It is so much easier to see it from the outside, and there are almost always good times in everybody relationship . It's not just his behavior that makes me concerned things have gone way too far, but your behavior as well. You exhibit some of the behaviors of people who are being treated abusively at times. I think you need to look at why you stay in this relationship when he abandons you so much, to the point you are becoming numb and he is escalating. It's clearly not working for you and doing more of what you are already doing isn't likely to work either.
Many people here have been where you are and tried to bend over backwards and scream I love you to a PTSD sufferer. It does not work and it harms both of you in the long run.
If you insist on staying in the relationship, then the best thing you can do is to let him be responsible for his own healing.
This is incredibly hard to do. Most people can't do it, especially not without any outside support.
The next best thing you can do is to go to therapy, and read up all you can about how to set boundaries. Things will get worse when you start setting boundaries - but that's to be expected and part of the process of healing from PTSD. It is why you will need the support network.
Until you are ready to take these kinds of very hard steps, it is not healthy for you or him to expect your relationship or his PTSD symptoms will improve, no matter what you do. In fact, you should expect that it will get worse as time goes on.
Even with these steps, and lots of treatment and support, this will be a life long battle. It's not wise to stay with the hope of him improving. You can't change him and he may never change. Before you keep investing in the life long battle, it is important to look at why you do these things - for him, or is it more for you to avoid the hellish pain of saying no to him and letting him reach his rock bottom?
The stronger and more supported you are, the better for both of you.