Though the Countess is standing by her man, she tells PEOPLE: "He screwed up"

Why I'm Marrying My Fiancé After He Kissed Another Woman: Countess Luann de Lesseps Tells All

The Real Housewives of New York City‘s Luann de Lesseps is not allowing one bad decision by her fiancé to destroy the love they have for each other.

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“It felt like someone ripped my heart out of my chest,” she tells PEOPLE of seeing the photos. “I was devastated. I had my heart broken on television.”

Despite his locking lips with another woman the night before the couple’s engagement party (de Lesseps reveals they’d had a fight and parted ways), the 51-year-old reality star is choosing to move forward with her engagement.

“I’m not going to let a stupid kiss ruin the rest of my life,” she affirms. “He screwed up. What he did was wrong. But this wasn’t premeditated. It wasn’t an affair. It was a mistake. He was upset with me. It was a stupid retaliation of some sort. He did the wrong thing, and he totally recognizes that. I know in my heart of hearts that he loves me.”

D’Agostino Jr. also realizes that his actions were a mistake. He tells PEOPLE, “If I could take it back, I would,” and adds, “I deeply regret the mistakes I’ve made, and most of all hate the way it hurt Luann.”

Though de Lesseps has made peace with her love’s indiscretion, she says she would not tolerate history repeating itself: “Obviously, if it happens again, I would have a serious problem with that. Fool me once, shame on you; fool me twice, shame on me.”