Locked phone suspicious?

Okay. So I need some help. Lately these past few months, my husband has been acting weird. So we both have a iPhone 6. And usually i wouldn’t think it’s a problem but he can use my phone anytime and I don’t but lately he has been heavily guarded on his. He locked his phone. He puts it under his pillow. Plus his sleeping position has changed where it’s like he hides his right arm under the pillow. I noticed that he turned off his notifications too like he used to get a text. I can see it and he will be like reply. One day, his phone was ringing and it was a number so I was gonna answer it but he ran so quick to me and was like don’t answer it. It’s a annoying relative. I was like wtf. So I began to write down the weird behavior. He recently also took this new job where I know it’s a lot of ladies there and my uncle is there too and he cheated on his wife. Weird right? So I’m guessing he is cheating on me. I asked him about it and he got very defensive and starting saying I’m “nagging” and now I’m being “insecure”. I even went as far as asking him to unlock his phone and he did not budge. I dontknow my husband at this point. I really wanna unlock his phone while he is sleeping just to confirm my suspicions because I know I am right about this. I wanna unlock it. Screen shot it. And see. I need evidence because clearly he gonna lie until I don’t have proof. How can I get through his phone??? (iPhone 6 and he has a passcode and Touch ID)