"I did not cheat on Matt. I would never, ever cheat on Matt. He was my fiance," Lamas toldPeople in a Tuesday report.
"I want to clear this up 100%. That [Vegas trip] had nothing to do with our break-up. I was in Vegas with friends. Matt and I had already broken up. I was a single 22-year-old woman having fun."
Grant and Lamas confirmed last week that they called off their engagement, an announcement that came a few days after a report first surfaced that she had traveled to Vegas and cheated on him with Wenerger.
While it was also reported Lamas broke-up with Grant via a phone call upon returning from Vegas, she claims they had already split before the trip and just delayed announcing the break-up until after she'd return.
Grant presented Lamas with his final rose and a marriage proposal -- both of which she accepted -- during The Bachelor: London Calling's pre-taped finale broadcast in May. Lamas then insisted she and Grant were destined to walk down the aisle together during a post-finale interview with Reality TV World.
Although a wedding won't be happening, Lamas plans on keeping the 2.85-carat Tacori platinum-and-diamond eternity ring she received when Grant popped the question.
"I have it and I am going to keep it forever for the rest of my life," she told People. "It's safe and clean and in a glass box like a glass slipper."
In addition, Lamas said Grant doesn't oppose her keeping the finger bling.
"Of course [he doesn't object]," she told People. "He wants to come over and look at it."
Lamas said she and Grant still talk "daily" even though their romance is in the books, and she plans on being "single for a while."
"If I find the man, I'll do it," said Lamas when asked by People if she plans to get engaged again. "But I'm going to give this the two-year test. And then marry him. I think I've learned that two months is a little too short."