Couples and phones

My boyfriend and I have been going through some serious trust issues. With that I allow him to go through my phone but when I ask to go through his it’s a big deal. He says that I never let him go through mine, which is not true, and that he’s not hiding nothing. He always put on the big spiel on how he was raised right and he’ll never cheat on a woman he loves (me) and all that but it always seemed too good to be true. Well, I went through his phone today and at first I didn’t say anything because I knew he’d be mad at me, but I found some dirt. He was FaceTiming a girl the year we met on Chris and taking pictures and screenshots with her and his nephew. He never FaceTimed me then because he said he was busy. When he asked me what was wrong I told him and he got pissed because I went through his phone. Am I wrong? Should I be mad? This girl is also someone who he says he’s “just friends” with but I don’t believe that bullshit. I’ll send the screenshots to show just how much fun they were having with eachother!