Im going crazy... please help me...

Long story short: bf cheated, I got over it, now he is secrative over his phone, hiding it when he is in the shower, messaging in the toilet/loo, people I dont know. He deletes his message chats. Im not allowed to see his phone. He wants his phone to be private. AND I think he is cheating. How can I tell if he is cheating on me?Im so confused my hart and my head are in a constant battle. I dont want to use this form really for my problems but I feel this one is getting to me and I need to know how to move past it.Okay long story short... Ive had 2 boyfriend. 1st one never had trust issues, 2nd one its an issue. My current boyfriend chatted to my Ex on Grindr and it wasnt agreed between us that we where going to keep useing the app. We agreed to not use it and he did, and he always told me he wasnt and I trusted him. So basically my bf now was my friend who outed my cheating ex.Then we where together for a coulle of months then my current bf basically cheated on me too. I dont know if it was phisical but it sure was on an emosional and intelectual scale cheating. Lets not get into that. So my issue is I have trust issues because of my bf, right? I thought I moved on. But he does stuff that makes my mind go crazy.I love him dearly. To the very most single celled organism in my body to the biggest star in the the universe.This started to be an issue for me a week ago. He chats to people on facebook, but he is secrative about it. I dont know what they talk about, who he talks to. He turns his phone around at night so I dont see messages coming in. He goes to the toilet to chat to them. Is a phone an issue in all relationship? I dont mind if he looks and my messages even while im chating, but he does and I cant understand it.Why hide? Is it because he is afraid I see his cheating.... these are the questions I ask myself and I cant sleep or think about my uni work because of it.