It is definitely a dilemma. Me and my wife both have PTSD, we both support each other as a carer and sufferers, but sometimes things happen and we can't both support and need supporting at the same time. It's like we help each other to heal and together we've come so far. But sometimes there is a shark, and sometimes one of us can pull the other and the other can pull the other and then we're both swimming, but sometimes we just cling to each other and we start to 'drown'.
Fortunately these don't happen too often, because we are constantly working on methods on how to manage this when this happens. In the beginning these would happen nearly every other day, now they happen so rarely! The less frequently they happen the prouder we feel about our accomplishments and how we manage and work with each other to reach this! Acknowledging even then that we aren't finished working yet.
So! We are both the carer and the sufferer in this area. And whenever we hit a speedbump we just go back to the drawing board! While drawing out plans for what to do when that speedbump occurs we focus on methods of healing, and where to move next.
If I could visualize what our drawing board looks like its something like:
Okay when this happens we go to step A --> B, and when B happens we move to C, when A happens in combination with D we have to move to F, because F isn't the same solution as E something like that.
Basically! PTSD is something we have to live with, and it IS finding the balance while healing along the way. What you can give and what you can't give, and even finding a neutral spot, where you're passively giving/receiving without even realizing it until you find both of you have managed to stop crying!
I have learned that there is a way to be both the carer and the sufferer at the same time and have the support be mutual. I don't know how to explain it because it's always changing, and it depends on whats going on/happening. But basically being 'aware' and 'presentation' really makes things easier sometimes. (Presentation of how you present how you feel, if one person is freaking out instead of going OMGGGGGG changing the tone, and the way you say it and even 'moving' from negative to positive 'focusing' after acknowledging the Negative, really can help both people at the same time including yourself without pulling the other deeper (and if they come through they will start reinforcing it back to you!), at least...so I've found in my situation.).
Just it's possible to manage at the same time, but for the times when methods slip by and we start to cling and drown. Well...that's what the drawing board is for >,<.