Zachary Woods popped the question to the PEOPLE.com blogger on the couple's one-year anniversary on Jan. 28, at home in front of their families.
"I still cannot believe I get to marry my best friend. I look at him and think 'Wow, how did I get so lucky?'" Smith, 20, who is based in Portland, Tennessee, tells PEOPLE. "He's everything I've ever wanted in a man."
"At one point in my life, I thought so poorly of myself and always said I would never find someone," she adds. "I never thought I would be happy."
Courtesy Kaitlyn Smith; David McClister
Smith, who weighed 414 lbs. in high school and lost the weight naturally through diet and exercise, says Woods, 23, stood by her through some of the hardest times of her life: her skin surgeries.
"He's seen me at my absolute worst and still managed to make me feel like the most beautiful girl," she says. "He's the true definition of a gentleman. He's honestly my best friend, my rock and my better half."
The couple, who were friends for a year before dating, now influence each other to live healthier.
"He's big into health and fitness as well. He motivates me daily. We workout together and enjoy it," she says. "He's always up for trying my new healthy recipes and 99 percent of the time, he likes it!"
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"I've actually gone once already and it was an amazing feeling just seeing the different styles on me now, and seeing them fit without skin showing through or hanging out, " says Smith. And if the dress she chooses exposes the scars from her surgeries, "I won't mind," she says. "It's me, it's who I am. It shows my journey. I'm not ashamed of my scars at all, I'm actually proud to have them. I've come a long way."