I get this. I do it too! I even understand your reasoning that you do it as evidence to yourself that the abuse happened. Somehow it can be validating to awash myself in the memories to feel the grief, the fear, the panic again while reading the messages or looking at photos, as if it reminds me why I feel so hollow and empty inside. As if by doing it says, "This really happened to you and you still need to process these emotions, you're not making this up". My mind has a fantastic way of pushing out the ugly thoughts and memories, of blaming myself for the bad stuff while simultaneously downgrading the actual event, practically absolving the perpetrator of any wrong doing. I think that's common for survivors of abuse of any kind. "Maybe he actually didn't view it as rape" or "Maybe he was too drunk to recognize my screams and struggles as actual fear" or "It was only sex after all, maybe I'm making too big a deal out of this, maybe he thought we were having fun and I'm a prude". When I read messages that he sent me after, or look at photos of him it brings a clearer focus of him and my memories of the event into my mind and in that moment with vivid certainty I know it WAS rape
I don't know that it is a healthy thing to do. I'm sure a therapist, as they have in the past, would tell me to delete them but I feel like I need them. Maybe I need that reminder. I also tend to do this when I am in a deeply depressive/isolated state and maybe also, as scout86 mentioned above, need it in order to numb out which can indeed feel safer than depression.
It's strange the things we do to cope. I've done much weirder things for sure; but that's a different post for a different day...;)
I agree though, this forum has been so useful for me. I don't get to get on here often but it's nice to be surrounded by "others" and not just that but "others" that are fighting and not giving up, who are getting better.
Maybe my post isn't relevant to your experience at all but I feel like I do kind of relate.