Accusing me of cheating 🙄

Am I the only one who is dating someone who was cheated on in their past relationship and now assumes you're cheating on them all the time because of what their cheating ex done in their PAST relationship 😠 So annoying my partner is always accusing me of cheating when I literally do nothing! I could be going for a drive and he will instantly assume I'm going out to cheat on him. I've told him multiple times I will never do that and he just doesn't listen. What do I say to make him believe me?!!!