How do you trust???

I’ve been trying & trying to trust my boyfriend, but my last relationship made me so insecure. Whenever he’s not answering, I feel like he’s with another girl doing something he’s not supposed to, even though he told me what he was doing. It’s eating me alive, & I haven’t accused him of anything because I feel like it’ll ruin my relationship. I love him, & I really don’t want to mess this up.