So you are in a common law relationship, right?
They may be requesting more evidences about your common-law relationship(it may also be something else.). But if they are indeed requesting documents regarding your relationship, gather as much evidence as you can and send all of them in. If you guys have any ongoing plan to get married soon, also tell them about it. I don't know how long it takes for them to attach the new informations to the file, but in any case send it to them as fast as you can.
Good luck to you, pls keep us all posted.