Jealousy advice please?

I’m a very jealous person. I’m afraid my SO may look at someone who’s attractive and would rather be with them then me. Or looking at their butt/bust. And thinking they look better than mine. I have been cheated on, left for someone else, etc. I don’t know how to feel. He said he wouldn’t ever do this stuff but I just wish I could control my jealousy and just not care as much about stuff like that. You know? Advice on how you coped with jealousy or something would be helpful here. Thank you!