The former boy band star, who split from the 28-year-old MTV presenter in June after three years together, is delighted to have rekindled the romance.
He said: "I am happy in a relationship. I was single for a minute, there, and then we've kind of patched things up. She is a very smart girl. She's far smarter than I!"
The couple took time apart to reevaluate their relationship, but quickly realised they couldn't live without each other.
A source explained: "They've always had a lot of love for each other, but they took a little break, and now they're working on their relationship."
The pair sparked rumours they had reunited in August, when they were spotted passionately kissing during a night out in Los Angeles.
Nick, 35, said in September: "We're trying to figure things out. I don't pretend to know what the future holds, but everything's good. Vanessa's a good girl, and I care about her a lot."