No. You didn't cause this to happen. If your relationship was secure, you wouldn't be afraid to introduce your partner to the hottest person in the world. The fact that you will be worried going forward, is a sign that your relationship is toxic.

I wish someone had told me that 15 years ago, when I decided to stay with the cheater. Even if they never actually cheat again, the root issues that caused that person to cheat in the first place, have caused me endless grief.

I understand now that cheating on a partner is a sign of having toxic beliefs about your self-worth, self-respect and/or shame. These can be undone I would say for 100% of people, however it can take years of effort and suffering in the interim, unless you happen to be able to fast-track with a good psychologist.