Hey! I am a wife of Complex PTSD, and a new one at that. Our last year has been a roller-coaster too, so know you aren't alone.
I was just wondering who said you don't need to understand? I tried the approach of put-on-a-nice-smile-and-always-be-the-glass-half-full-wife for a while until a few large episodes and much tears, debate, etc. helped me realize that the thing my husband wanted most was for me to act out my love/acceptance/caring about him by learning what he deals with. Nothing frustrates him more when he is dealing with something that I don't understand and he has to make himself even more vulnerable and explain his deep pain and suffering to me. I am sure that all people dealing with this are different, but that was a huge realization for me. Another part of that realization was that I need to put into practice the understanding. By that I mean, not blaming my husband when something triggers him and an argument is started out of nowhere. Or, for instance, understanding that by talking a certain way, it triggers his abandonment issues from his mother so I try to avoid that.
I am sorry that you are feeling so lost right now. It's a crazy thing because lots of times, there really isn't much you can do for the one person you love the most. You can't reach out to them because they don't want to be touched, but you would never even walk out of the room when they are struggling because you know they want you there. You can't help them because at some times, there just is nothing you can do, so in ultimatum, you sit there. You hurt because they hurt so much and yet you can't do anything about it. It isn't fair to anyone. I would suggest to continue learning as much as you can and putting in work. The other part is feeling out where your husband is in his struggle with PTSD. If he stopped seeing a therapist, it may be a long haul for a while, but there were phases with the struggle for my husband. I would just try to be prepared with good counselors for him to see when/if he arrives at a point where he is ready for it and in the meantime, find a support group.