6 Things You Didn't Know About Fun., Bleachers' Jack Antonoff

— -- intro: You might not know Jack Antonoff by name, but you have definitely heard his music.

As a guitarist and vocalist for Fun., he co-wrote two of the band’s smash hits, “Some Nights” and “We Are Young.” He’s the man behind Taylor Swift’s “Out of the Woods” on her new “1989” album, and he wrote Sara Bareilles’ hit single, “Brave.”

Now, Antonoff, 30, is stepping out on his own as a singer/songwriter with a new band, Bleachers, which already gotten noticed with their insanely catchy single, “I Wanna Get Better,” and their new hit, "Rollercoaster."

“I just work a lot,” Antonoff said in an interview with “Nightline.” “I just remember recording in a hotel room in Malaysia. I work on planes, I work on buses. A lot of times when I’m backstage in the hotel or on the bus, I would have new ideas. It’s just nice to constantly be working.”

Antonoff spent some time with “Nightline,” in which he talked about his journey to the top of the American Top 40 charts and his relationship with “Girls” creator and star Lena Dunham. Here are a few things you might not have known about Jack Antonoff.

quicklist:1title:He Lived in His Parents’ House Until He Was 28media:28040173text:Growing up in suburban New Jersey, Antonoff said he slept in his childhood bedroom until about a year and a half ago. His girlfriend Lena Dunham, he said, is the reason he finally moved out of his parents’ house.

“Until very recently I felt totally uncompelled to move out, which I think if I look at it, like psychologically, I want to I wonder if I was so independent on tour that I just never cared to leave,” Antonoff said.

The couple now shares an apartment in Brooklyn.

quicklist:2title:He Grapples With Anxiety and Depressiontext:When Antonoff was 18, in rapid succession, the 9/11 terrorist attacks happened, his sister died of cancer and his cousin died while fighting in Iraq.

“At that point in life, that’s when you’re supposed to be carefree and think that the world is wild open and anything is possible… I had the opposite experience,” he said. “My world felt very much closed and it felt like anything horrible was possible. … To this day, I still have very intense anxiety and depression.”

quicklist:3title:He Briefly Dated Scarlett Johansson text:In his teens, Antonoff said he became obsessed with music. By the time he reached high school, where he said he briefly dated Scarlett Johansson, he was playing in bands.

“Every time I played a show I would write down the date, where it was, how much we got paid, where in the bill and who else played,” he said. “The first time I got paid for a show was ... January 18, 1999, the Fire Hole in Bolton Town, New Jersey. We played first and got paid $20. The next show we got zero. … There’s a lot of zeroes.”

quicklist:4title:He Doesn't Want to Stop Touringtext:Antonoff skipped college and struggled in relative obscurity for many years until he and two other guys started a band called Fun.

Within a year or two after Fun.’s 2008 debut, the band exploded in popularity and their songs, “We Are Young,” “Some Nights” and “Carry On,” soared to the top of the pop charts. In 2012, Fun. won a Grammy for Best New Artist and a Grammy for Song of The Year for “We Are Young.”

The band has gone on worldwide tours -- a life Antonoff loves, but admits can be hard.

“Touring is hard. I’ve never, I don’t understand when people walk away. It’s not for me,” he said. “At this point after 15 years it’s just a huge part of my life. For better or for worse, I just have to be on tour for some portion of the year. But it’s not easy you know. It’s not easy on the people you love and I understand when people look at this life and say this isn’t sustainable.”

While on the road with Fun., Antonoff started writing songs for a new band, Bleachers. Their first single, “I Wanna Get Better,” was a hit, and the music video was directly by none other than Dunham.

quicklist:5media:28040391title:He Says Things Clicked Right Away with Girlfriend Lena Dunhamtext:Antonoff said his sister set him up on a blind date with Dunham, and he instantly felt a connection with her.

“I think we passed each other’s tests,” he said. “I feel like for me in the past, dates were always really intense and heated and then they either didn’t work or they worked ... there was never any room in my dating history to causally date someone.”

quicklist:6title:He Doesn’t Want to Get Married Until It’s Legal for Everyonetext:Both Antonoff and Dunham have been outspoken in their support for legalizing gay marriage, and have said publicly they aren’t getting married until every state has lifted the ban.

“What I personally believe, to me, it seems odd to get married when someone else can’t and I always believed … that it should be a country thing,” Antonoff told “Nightline.”

But Dunham set off a firestorm of speculation when she posted a photo on her Instagram account this week showing her flaunting something sparkly on her left hand. Dunham told reporters at the “Girls” Season 4 premiere Monday that the “ring” was actually a stack of three friendship rings, and she and Antonoff were not engaged.