Bieber told The Sun's Fabulous magazine that his first kiss with the Wizards of Waverly Place star was the best he had ever experienced.
"[It] was the best of my life," said the 18-year-old. "It was in the car. It was scary and spontaneous and it was just awesome."
The singer spoke of his love for Gomez, who he has been dating since 2010.
"What does love feel like? It feels good," he said. "If you're really in love then you should get butterflies. Butterflies and happiness, that's how I feel anyway.
"But I never like to throw it in my fans' faces. I love my fans and I'd never want to do that to them. It's my private life and I like to keep separate. I don't have many things that I get to keep to myself but that's one thing."
He added: "I'm very happy. And I know my fans just want to be happy for me."
Bieber's latest album Believe is released in the UK tomorrow (June 18) and in the US on Tuesday.
Watch Bieber rehearsing for his upcoming 'Believe' tour below: