Adam Levine says the death of his manager was 'one of the saddest moments' of his life

Adam Levine is still mourning the devastating death of his manager and childhood friend, Jordan Feldstein.

The 39-year-old Maroon 5 frontman is named Variety's 2018 Hitmaker of the Year, and in the accompanying interview, he talks about taking control of his career after Feldstein died suddenly last December. Feldstein, who was the older brother of actor Jonah Hill, died of natural causes from a blockage of an artery in his lungs and a blood clot in his leg. The Los Angeles County Department of Medical Examiner-Coroner also listed obesity and pneumonia as contributing factors to his death.

"It was a tragedy foisted upon us and far and away one of the saddest moments of our lives, and personally of mine," Levine says. "This is a kid I’ve known since we were in diapers. He was one of the most important people in my life from a very early age."

Levine says he thinks about Feldstein every day.

"It will always be something that’s missing in my life," he shares. "I break down; I cry. We built this together, and it will never be complete without him. But at the same time, we know he wants us to keep trucking."

The father of two was forced to make tough decisions about the future of Maroon 5 following Feldstein's death, and chose to bring aboard Feldstein's business partner, Irving Azoff, and manager Adam Harrison to help manage the band. He also self-manages to a point, and says he doesn't engage the record company when it comes to decisions about Maroon 5's music.

"I’m almost 40 and have been doing this a long time," he notes. "I don’t need a babysitter."

"It was brutal," he also admits about restructuring his management team after Feldstein's death. "When that all went down, I remember having to dig deep and say to myself, 'Am I just going to let this fall apart, or am I going to try and hold this thing together?' In chaotic situations that are so horrific and so gut-wrenching, you have to kind of show up, you know?"

Levine's decisions have already proven to be sound, and he reveals he had to beg for their mega-hit "Girls Like You" featuring Cardi B to be on their latest record as a last-minute addition. He also talked about the importance of the video, which featured Levine celebrating female empowerment with celebrities including Jennifer Lopez, Ellen DeGeneres and Gal Gadot. The musician says having two daughters with wife Behati Prinsloo -- 2-year-old Dusty and 9-month-old Gio -- connected him to the plight of women.

"I have two young daughters, and to think about them being mistreated at all -- ever -- made my blood boil," he explains. "So we went for it because I felt that as long as I stayed close to my heart with this concept, I could never go wrong. … In the video, I was doing it for my kids and my wife. If anyone doesn’t understand the intentions, f**k ’em."

As for whether Maroon 5 is set to play their biggest gig ever -- next year's Super Bowl Halftime show -- despite the controversy surrounding NFL players who kneel on the field during the national anthem to protest racial inequality and police brutality, Levine remains cryptic. A source told ET in October that Rihanna turned down the big opportunity to show solidarity for Colin Kaepernick and other players.

"I’m still formulating a lot of things," Levine only notes.

The Voice coach is turning 40 in March, and says he actually has already achieved everything he's ever wanted.

"Bring it!" he says about the milestone age. "I mean, I don’t know, what the f**k else do I want? I’ve got a beautiful family, a beautiful wife, two beautiful babies, and I’ve got money in the bank, and I’m really happy with my career and my output and the person that I’ve become and the person that I hopefully will stay. S**t, it’s too daunting to imagine anything else. I feel like I’ve already achieved anything beyond my wildest dreams."