Always Thinking Any Love Interest Is Cheating

After being cheated on a few times already I am always in fear of the person I'm talking to sleeping with other people, sending them pictures, getting hickeys, etc. Like to the point where they could be going to a party and I'm terrified that they're gonna be with someone else. I don't think I'll be able to be in a healthy relationship while I'm like this. How do you get over this and let the past die?