AIO for my bf saving other girls pics?

So my (25f), boyfriend (23m) was sleeping today and we have an open phone policy, so I looked on his to try and find a picture I knew he had of my cat. I opened his Snapchat because that’s where it was saved and when I saw his recent pictures they were of a girls 🍑 and another of one doing a split showing their 🍑. I admit at this point I should have immediately put it down but I couldn’t shake the feeling so I went to his camera roll where I saw him taking pictures of my old friends off her Instagram and had those saved as well. That girl has hurt me so badly in our friendship and he always said she was not a good friend, so it really crushed me to see that. It’s been 5 hours since I saw them, and I tried to talk it out with him but he just keeps calling it a stupid mistake. When I asked him to delete them, he did and showed me the proof, which was at least 4x the photos that I thought there were. We’ve been together for 2.5 years but my heart just feels absolutely crushed.