Hi skybluePictures aren't much in the way of evidence by themselves. Try and back them up with hard evidence or at the very least, use photos that were not taken by yourselves.
Some examples we used: We go on trips often with friends (so flights, event tickets for the group, hotel/AirBnB, etc), out to dinner with friends often (photos that they share on their social media of us all together), joint invitations to weddings/parties/etc, we played social sports in our town so there are photos of us with our team on that website playing various sports, we volunteer together so can show membership with those organizations, we help out with our kid's sports and extra curricular activities as well as volunteering together for school events, etc. We're listed as emergency contacts for each other for work and other things, as well as at the school (including my in-laws on the authorized pick up list).
The sky is the limit. Do those around you know about your relationship? Do you go out in public? If yes, then think of how you could prove this. Tickets to events, photos of you together on social media or websites that you have no control over, proof that you both hang out together with other people, and so on.