The procedural fairness letter is the normal process CIC follows when they are about to refuse an application. In your case, you don't meet the common law requirements and they are providing you one last chance to prove that you do.
In other words, your application is going to be refused since you haven't lived together for a year since getting back together. The letter is really just a formality at this point.
You'll either need to get married or really become common law (i.e. live together for a year continuously) before you can reapply.