AIO- Found old messages on my bfs phone

So essentially me and my bf started started dating on November 1, we're in a LDR, and the other day he gave me his password for his discord. Previously I had seen he was messaging one girl, but they stopped by the end of november. So i let it go since the messages seemed like he didn't want to be there. Yesterday I found 4 other girls he was messaging, all of them ended in November with the girls ghosting them. He referred me as a "friend" to them. There was one girl he messaged in November, and she responded in January, and he messaged her back. Mind you, these were flirtatious messages that he was initiating

I told him that, it's one thing to message before we were dating, that's fine, but it's another thing to be actively seeking women out after we started dating.

I don't know what to do. I want to scream. Am i over reacting? or do i let it go since these happened so long ago?

edit: for more context- he messaged the girl in january, 2 days before he drove down to see me. and met my family. I see him about once a month for a week or so. he gave me his login infos for everything saying he has "nothing to hide" Apologized a lot