In my experience, it takes a long time and a lot of info to get a grasp on PTSD. Parts of it are well known - triggers, flash backs. But the depression, isolation, avoidance, numbing of emotion issues are lesser know, in my opinion. A lot of it goes against most people with "normal" brain's instincts. It's hard. As someone who dealt with being cut off several times, it is painful and has nothing to do with you. That's a difficult aspect to get, that it isn't personal. You can understand logically, but getting your emotions to accept it can be very difficult. My ex isolated for 13 months the last time. And that distance ruined what we had even if it wasn't personal. I'm try to be his friend, but I know that's all I can do. But every situation is different, PTSD is so individual. There are so many variations of the overall issue of dealing with stress and the trama(s).
Don't know if this has helped at all, but two things helped me the most the cup analogy and the fight or flight explanation.
You can find a lot of references to the stress cup, but basically all stressors compound for people with PTSD. Good, bad, it doesn't matter. Stress is stress. Their cup can only hold so much.
Also, the explanation that with PTSD you can be constantly stuck in the fight or flight or the freeze mode. It's chemical within the brain, a reaction that cannot be controled. It can be managed and it can wax or wane, but it is there.
I hope my rough explanation of those two things helped and I hope I said it ok. But, those are the two things that got through to me the most.
Best of luck. If you ever need, feel free to mssg me.