Lori Diaz and Vinny Hickerson
12/02/2011 at 05:00 PM EST
Getting engaged made Biggest Loser
contestant Vinny Hickerson feel like he had "a million pounds of weight off my shoulders."
Figurative weight, that is.
Hickerson, 28, a singer in the country duo Trailer Choir, proposed to his longtime girlfriend, Lori Diaz, 29, during a date at the Grand Ole Opry that was filmed for the reality weight loss competition, and will air on Tuesday night's episode of The Biggest Loser
"I wanted to take her there because it's a place where so many dreams have come true, right there on that stage," Hickerson tells PEOPLE exclusively. "My biggest dream is to be a great husband and a great father, and fall in love."
"There was no one there but us and a camera crew," says Diaz. "We sat down in the front row and he gives me a spiel about how he loves me more than anything."
Hickerson popped the question with a ring from Nashville's King Jewelers. "I thought it looked like the Eiffel Tower, which makes people think of beauty and romance," he says. "Just like the first time I saw Lori, out dancing in a zebra dress, I had that same feeling like, 'Oh my gosh, this is the one.' "
The second biggest surprise of the evening? A private concert by the country group Thompson Square
, who played their Grammy-nominated song "Are You Gonna Kiss Me or Not."
"I couldn't believe they were there just for us, in this huge, amazing place," says Diaz.
Hickerson has been open on the show about his goal to lose weight in order to become a fit future husband and father to Diaz's 9-year-old son, Brennon.
Before, "I wasn't out playing ball with Brennon and even watching him skateboard. I'd just sit in the car and watch," says Hickerson, who is down to 314 lbs. after starting the show at 426 lbs. "Now, there isn't anything I can't do!"
Adds Diaz of the proposal: "I'll never forget that night for as long as I live. It was so perfect, even more perfect than if I had planned it myself!"