Hmm, well, if he's explicitly said, multiple times, that he wouldn't want to know, maybe he really means it. I have an obvious strong bias for honesty, for a number of reasons, but there are sometimes nuances.
As for my story, unlike LR's and others whose stories I've read, it didn't go straight from cheating to poly, by any means. I *did* cheat, reveal it, and get forgiven, though, as I said.
Many years ago, I dated Davis. After two years, I slept with an old flame, Ziggy, with whom I was still in love. I told Davis immediately, he was very upset but was willing to move forward together. I had a very rough week deciding what to do -- Ziggy would have been willing to share me, but Davis, who had never even remotely considered the idea of an open relationship, was not. In the end I stayed with Davis for another year, but I pined for Ziggy and our relationship suffered.
Eventually I left, reconnected with Ziggy, and found myself single when that didn't work out. Davis and I remained close friends, then eventually FWBs. I began dating Gia around this time. Davis, one day, suggested that we try a "real" relationship again. I told him that I wouldn't leave Gia, and that he had to decide if he could handle a poly setup. He did a lot of reading and thinking and decided he could. It's been over a year now since he and I have been together again and we've had no problems on the poly front.
A big part of the reason that Davis and I are able to do poly, even though the idea didn't come naturally to him, is that he trusts me completely. Even though I broke his trust in the past, I then looked him straight in the eye and told him, and I know that fact means a lot to him. The knowledge of my infidelity hurt him for a long time, but being deceived in an ongoing way would have been a very different and, I believe, more damaging sort of betrayal.
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.