The guitarist reveals he didn't know much about Girls creator and star Dunham before the 2012 date, so he made sure he did a little research before going out with her.
He tells New York magazine, "It was a blind date by modern standards. I mean, I used the Internet (to find out more about her)."
Antonoff, who dated Hollywood beauty Scarlett Johansson in high school, needn't have worried - the pair hit it off straight away.
He explains, "I told Lena everything about my whole life, because when you really like someone, you want them to know everything about you."
The couple is now looking towards the future and Antonoff reveals he is eager to settle down and start a family.
The 30 year old says, "It just seems like the most fun thing in the world. I've never met people who have kids who haven't looked me in the eye and been like, 'It's the greatest thing that's ever happened.'
"I'm not, like, 24 or 22. I'm no longer in the phase of my life where I talk about everything as in the future. Like, I'm in the future."
However, the musician admits he and Dunham are so busy, they may have to wait a while: "It's hard to imagine when the right time is because things are so crazy at the moment."