There is a simple method to begin IF communication is a difficulty. You place a notepad on the table and you both write, periodically, into the notepad what you feel. You create agreed rules together, then you leave the book. If communication become difficult, you revert to the book. Write what you feel, write what you want to say, but can't get through, and leave it for the other to read in their time, process, then respond.
It is a simple, basic way to communicate about important issues within the relationship. It opens the dialogue, in essence, and when you can both communicate face to face more effectively, you don't need the book any longer. But it stops many arguments and such, words said in the moment. Writing what you feel, want, need, also puts a record for each other to then point out problematic communication wording, where one may attack a little, make snide remarks or such. So it makes you both think before you write, whilst you write, to ensure you aren't repeating the same mistakes that are being made in verbal communication.
Like said, when you master it and have a great communication style going in writing, helping one another to see each other more openly and honestly, without negative communication methods, then you can put it away and transition your new style verbally.
Again... that is a very basic one where communication has gaping issues, and basically, one or both are attacking each other more than effectively communicating your feelings and concerns.
Also... if you get the above linked relationship book, it is better if you read it together. You set aside an hour each night where you both read to each other and discuss what is read. You might only get a few pages done a night with the discussion, within the hour time, but it is a way to start from the basics and transition together. It is really important that you both change together, because that is part of the problem in a PTSD relationship. Both have their normal, then one gets PTSD... massive change in dynamics, the relationship turns to shit as a result. Again, not a fault, just the realism of what happens when one changes significantly in a relationship, not both. If two people actually get PTSD together, you would find less issues as a result because you both would be in similar places.