My boyfriend doesn’t trust me, what’s your thought on this?

Hi everyone, my boyfriend doesn’t trust me, he always think I’m up to something silly, he thinks i’m cheating on him, the whole trust issue started after he found out my ex was still stalking me, I have blocked my ex in every way possible for him to reach me, but my bf still thinks there is something up, I have tried to let him know I’m not cheating but he still has that mindset of me cheating, please what should I do to let him know i’m Loyal to him? What’s your thought on this?

PS: I’v made my research to know if he is the one cheating and I found out he isn’t aswel