The Saturdays artist, 41, split from David and model Sian Osborne back in March.
Una confirmed she imparted her ex to another lady, yet said she was "duped" into being in a throuple, and left the relationship when she understood.
Also, on her choice to revolt against it, she conceded: "I feel eased I must say my piece.
"Reality directly from the source."
Una tended to her experience on Vogue Williams and Joanne McNally' digital recording, My Specialist Ghosted Me, and she made sense of she met David through a dating application.
She shared: "Dating HIM is the right term since that is the way things were, it was anything but a throuple. We had a wonderful relationship.
"It was easygoing, it wasn't significant. I was cheerful enough with it. It was in a heartfelt limit.
"He was exceptionally fair that I wasn't the main lady he was seeing, I was extremely mindful he was seeing others. I realized he was tell the truth and dislike I was being undermined.
"I realized he wasn't spouse material, only a tad of tomfoolery and I was getting a charge out of it."
David, 42, and Sian, 30, got together in 2020 and invited Una into their relationship toward the finish of the year before.
Be that as it may, Una - who split from Ben Foden in 2018 in the wake of learning he had cheated - reviewed: "I straight out asked him 'what are you searching for?'
"Since I did a Google and thought 'I'm presumably going directly from the griddle to the fire with this one since he did precisely to his better half how my ex treated me.' I could have done without that."
Asked by web recording host Joanne in the event that David realized it was a "throuple", Una said: "I think he was extremely blissful about it yet I was in bits about it.
"He didn't get it, he was continuously attempting to mentor me on how not to fly off the handle yet I've never needed to stir things up around town button to such an extent.
"I had a rundown of words hindered on Instagram.
"I would rather not be in a three-manner relationship!"
At the point when Joanne summarized it as, "you were duped into a throuple" Una answered: "I was!"
Una said she chose to cut ties when she understood David "didn't completely accept that the customary relationship exists any longer".
In spite of their precarious relationship she has stayed friendly with David.
"I truly enjoyed in my relationship with him," Una said.
"He was exceptionally kind to me and extremely fair however it ran its course and I've been single from that point forward."
They have a daughter aged ten, and son, seven.
Last month, David uncovered he had supplanted Una with a dazzling personal trainer in his throuple relationship.