Welcome Sairadance.
I totally appreciate your position and find trying to understand PTSD as being like trying to comprehend a different way of life at times. The hardest part is when the person you love disappears and someone else replaces them who is distant, less affectionate and sometimes unapproachable. It can be very confusing. I find it is hard to leave them alone and give them space to de-stress when all you want to do is put your arms around them, hug them and do something to help.
While a PTSD suffer has to help themselves it can be heartbreaking to watch as a partner. I have found that while a sufferer is going through a stressful time they inadvertently shut out their partners and it is hard to understand why they "don't seem to love you as much all of a sudden".
I am still learning but one thing I do understand is that as much as you want to help, the best way to do that is let them help themselves. It can be difficult to accept but a harsh reality

.
While the road with a PTSD suffer can be bumpy at times, the ones I know are worth it

. Good luck in finding your own understanding.