I just read the OP's other thread. I think the other posters are being a little harsh, polycouple. That's what we do here, tough love, and certainly it's better to be honest if a boundary was broken, but knowing the history of the situation doesn't change my take on it significantly (I assume you were sincere about your remorse and it didn't happen again, at least?).
If anything, my biggest new piece of advice based on reading your other thread is that I think y'all moved too fast. It's *hard* integrating a new person into an existing relationship, there are sooooo many dynamics to work out, and to so quickly start spending 5-6 nights a week with one of the members of the couple you're involved with... well, I can see how whiplash happened for the other member, and how things just didn't go smoothly, especially since it sounded like you guys prioritized sex over the hard work of talking out your feelings/fears/desires and figuring out a setup that would actually work for all involved.
Slowing down and more long, deep talks should have happened earlier. Hopefully it's not too late for them to happen now. Be brave. Equality is a great goal but it takes significant time. Are you interested in or "allowed" to date outside them?
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.