My bf is in touch with his ex sex partner

My bf slept once with his friend. They have common friends, they work together 1-2 times a week. When i found out I cant sleep peacefully since. I know he loves me, but I cant stand that he has contact with someone who he has seen naked. I feel like he can compare me to her in his mind and i feel uglier. And if he once was attracted to her, was horny about her why would it change now? Please tell me if i have right to feel uncomfortable. I really overthinking a lot, she appears in my dreams and im really going crazy i dont know what to do. Im so tired