[thinking out loud here, with apologies if this sounds a bit impersonal]
My future husband is [UNDIAGNOSED] complex PTSD dissociative (repeated developmental trauma/abuse/abandonment/violence), to the best we can tell. Not to the extent of DID, but we have had at least partial [fragmented?] "others" in our relationship. AND we think I am somewhere on the "more than normal" end of dissociative experiences, too. We both have serious "attachment issues" (of a somewhat opposite nature) and have had various bad "core beliefs" that we have both worked hard, and WITH each other, to find healing and good communication ..
BOTH of us have had to go through various forms of counseling in our lives .. BOTH of us know that my "issues" are real and needed addressing, but were nothing nearly as severe as his .. This means I am his "Supporter" but HE is my CHAMPION. :) I have a kind of "counselor's mind" but he also has very practical wisdom learned through the school of hard knocks, and we meet in the middle between having our heads in the clouds and our feet firmly on the ground. ;)
And my knowing that I have things, too, has forced me to learn greater humility and not be so over-confident about whether I'm reading him or our situation altogether accurately, and HIS issues have force him to be extra careful with me, cuz he knows his "fight or flight" response is LOUD and often uncontrollable, and he has refused to commit to things at varying times because he doesn't want to "break his word" with me. This usually works for us, because the HEART of the man is honorable, even if his actions are confusing and difficult sometimes. (and even if I bring my issues to the table) .. I have to fight with myself (!) whenever I'm tempted to doubt his INTENTIONS, because I do in fact BELIEVE the best about him, at all times. Walk myself through our past history, test my assessment of his past proven character so that I'm not overruled by my "emotion" in the moment. ... etc. And I still gotta work on me to SHOW that I believe in him, wrestle my own frustrations, etc. into submission. "Take every thought captive" so to speak.
It really helps to have "rules" of behavior, under the protective umbrella of unwavering commitment to one another and unconditional love. "I'll work through this with you NO MATTER WHAT because I BELIEVE in you, even if we have issues, and I want to be WORTHY of your trust." I think ALL relationships would benefit from this kind of structure, cuz as was already stated, we ALL "have issues." None of us was parented perfectly, or treated perfectly by others in the world. My guy discovered, "accidentally" in his work life, that he was best able to "function" normally when he was adhering to a hard and fast "policies and procedures" manual (applied "firmly, fairly .. so we have kinda adopted this for US, our marriage, any future parenting we will do to ensure we don't pass along the "attachment" issues to our kids, etc. We will have a "Family Covenant" to govern our behaviors and decisions .. and we are EXCITED by what we've come up with so far. This idea might not be for everyone, but each couple is unique - the point is the commitment to work it through together.
"I don't quit you. PERIOD."
I hope you find what you are looking for!!
~WU