I'm a supporter, not a sufferer, but I may be able to offer some suggestions from the "other side of the coin." Keep in mind this is just general, and not specific to any one person or relationship. I know not all sufferers and supporters go through the same things, but from observation and talking to a lot of supporters on here, there seems to be some commonality in a lot of PTSD relationships.
A sufferer's rough patches are their supporter's rough patches too. When our sufferers are stressed and triggered, we also deal with the stresses and triggers in our outside way. While we don't go through the horror and pain that sufferers do, we do worry, stress, and feel helpless or useless to our loved ones. Unfortunately we also seem to bear the brunt of lashing out. Isolation is necessary for sufferers, but it makes a lot of supporters feel abandoned and uncertain. For the most part, we know our sufferers don't mean it and can't help it. They have to do what they need to do to cope. It's all part of loving somebody with PTSD.
Caregiver or compassion fatigue happens to the best of us. It doesn't mean either party is wrong or bad, etc. It just happens. From a supporter's point of view, it seems like you give and give and give all the understanding and compassion you can to your sufferer, but one step wrong on your part and it all comes crashing down on your head. This is especially sucky when you are dealing a bad patch and it happens a lot in a short period of time. Those of us in long term relationships know that our sufferers cannot deal with a supporter's feelings when they are in the midst of it all, but still, after awhile it wears on you.
I've been there with my sufferer. Again, I don't know anybody's personal situation, but I can offer a few general suggestions. Firstly, a little compassion goes a long way. Sometimes just hearing that you are loved and appreciated works wonders. When you are busting your butt to be a good supporter, having your hard work recognized can be nice. An "I love you" is never bad. When you are taking care of all the mundane things of life because your partner cannot deal with it, it is nice not to have things made more difficult.
Cutting a us a little slack is probably the most kind. We have emotions too... we have bad moods and don't feel like dealing with *it* at times. Our feelings get hurt. We get worried sick and may hover or be clingy. We get sad. We get scared that our relationships will end. We get angry when lashed out at and want to fight back and defend ourselves. When a supporter is usually pretty good at dealing with these emotions, it is nice to not have those bad moments rubbed in our faces or blown up into a big thing when we do lose our composure. Acknowledge that our emotions are valid and important too.
Also, knowing how difficult it can be for a sufferer to do any of this when they are not feeling well, the sheer effort it takes to do any of these things is also a big sign of how much they care about you and can mean the world.
Just my two cents. Good luck with your partner.