Cheaters eventually get caught

I 36 f have been in a relationship with 31 m for 4 years now lately he cares more about his appearance hides his phone got mad and threw mine I was letting him use and since I knew he was using it to talk to other people I broke it well he has been asking to use mine and I’m finding random screenshots in my photos and websites that are different from what they say they are can anyone tell me how I can find out if he is hiding something behind the screenshots he took because he has tons of them on his work phone