Hi Dave3,
JandM is right. INZ look at evidence that a couple have been LIVING together. My partner applied for partnership visa of a worker visa. We have been together for 1.5 years before we applied for the partnership visa in April 2018.
We provided the below documents
1) A letter outlining our relationship, from how we met, to where we have been, how and when did we meet each other's families, if we have common interests, and our future goals such as starting a family.
2) Flat Share tenancy Agreements
3) Bank Statements - to show that we are financially interdependent on each other. Highlighted Incoming(Salary), outging (Rent, utility bills, grocery shopping)
4) Our facebook messages, not all of it, however it is to show communication between us from the start to current status
5) Photos of us in different countries, with our families - We have written the country, the month and year the photo it was taken
6) Bus tickets, flight tickets etc to different countries
7) References from his family, my family, his friends and my friends - to show that our relationship has been recognized by them that we are in a stable and genuine relationship
8)Screenshots of our facebook/instagram to show that we have publicly recorded our relationship
9) Assortment of birthday cards/Valentine day cards/Christmas/Anniversary cards during our relationship
Hope these helps!