I'm really happy to hear you say that.
Anybody can screw up and make a devastating mistake. It takes a lot of courage to admit it and take responsibility.
The most important thing here is what you've learned from this experience.
No, you're definitely not the only polyamorous person who realized what they were by cheating. Of course, as you know, it's about the worst way to come in to it, but now that you're here and what's done is done, you can find a better way to do it next time.
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker