I just found out my bf of over a year was talking to a girl a few weeks before me

I don’t know if this is that big of a deal or not but I haven’t said anything yet. I don’t really know what to do anyways or if I should do anything. So today I went over to my boyfriend’s house and he was sleeping and he’s usually doesn’t care if I go on his phone. So I went on Snapchat and was looking at past chats and I saw one from September 2023 from this girl named Abby and her bitmoji looked goth and I’m goth so I was like huh that’s weird. I click the chats and I see that they were flirting and send face photos and he was calling her pretty and stuff. I was confused and I saw the date and it was like in September and me and my bf started talking in late September. I’m just confused and I don’t know if I should say anything since it was over a year ago. What should I do?