Cheating Boyfriend

I found out my boyfriend cheated on me twice. It's a super long story, and I am completely heartbroken. He begged for a second chance so I gave it to him, but I'm having the hardest time trusting him again, and it's been 4 months. He keeps saying "if we don't have trust we don't have anything" and even changed his password on his phone so I can't look in it because he says I need to trust him. Do you think this is a good way of making me trust him or just trying to cheat on me again?