I can't see text messages working. That's not really proof of a relationship. We submitted a couple.of photos from each year we had been together, and in various places worldwide on holidays together. Photos of us at family functions, us with our daughter growing up etc. All photos had details of who, when and where on the back. Stuff with my family, with my wife's family and everyone. 2 letters from friends confirming we were a legit couple and history of how we met etc. Joint rental receipts, joint household bills, joint bank statements etc. Various examples through the years to show we lived together. Obviously marriage cert and daughters birth certificate showing both names. Any legal docs and historical photo evidence will prove a relationship, but text messages could be between any 2 people and don't really show anything. E.g. my wife and I could change our phone names to you and your partner and send our texts as evidence. It doesn't prove anything and would be difficult for them to verify the info as genuine and correct.