I think my (32F) relationship with my partner (M34) is over.

I think I already know how I feel about this but asking for some opinions just to help me clarify and move forward. I (32F) did the 'f around and find out' by looking on my partner's (M34) old phone and found a heap of messages (with some graphic photos/videos) between him and another girl from mid-2024 onwards. Called him out on it, he swears it was from VERY early on in our relationship before we got serious when he was having a hard time (so towards end of 2022) and it was someone he'd also been chatting to on an app around the time he matched with me, and the incorrect dates are due to a phone reset and backup (which google says is possible). We've been also having some other minor issues related to his past trauma just in terms of communicating feelings etc, but nothing else like this.

I really don't want to think he's lying so directly to my face. But there's photos clearly taken in our house (which was just mine before he moved in) which I feel yuck about. There is also possibly an object in the background of one of the videos that I didn't have in my house until 2023, but I'm not 100% sure and am not looking again. Is he lying about the timeline? He swears he isn't and has otherwise admitted to the fact it happened and shouldn't have. We've now been together 3 years. Typing this out makes me feel like I'd be stupid to trust him, but I don't even trust myself at the best of times and just need some thoughts independent of my messy head right now.