My boyfriend is acting suspicious with his phone

We have been together 6 years, we are currently 25. Well he has never wanted to tell me his password and years ago when I was younger I went through his phone and caught him msging a girl from high school. I was dumb so I forgave him, but I’ve noticed he still doesn’t let me touch his phone and when I do, he starts like panicking like coming towards me and grabbing his phone and telling me to stop if he thinks I’m able to get in it. Well i actually don’t know his password, but I saw him put it in one day and then last night he said if I know what his password is, I can go through his phone. So, I put his password in his phone infront of him and he couldn’t believe it he was SO shocked. And when I went in it I went to Snapchat and there was a lock. He put a lock on Snapchat so only he can get in it even if I were to go through his phone. He said he was just playing with the new features, and then he took the phone away from me and said I couldn’t look through it. Later when it was time for bed he left his phone (on purpose) outside in the car, and I KNOW it was because he was scared that when he slept that I was going to go through it. He says he just forgot it in the car, but he had it all night and right before bed he decided to leave it in the car. Idk what to do… he won’t let me go through it so if he is cheating I’d be crushed