The "Aaron's Party" singer passed away last November at age 34, leaving behind friends and family including his now-22-month-old son Prince. For Nick, losing Aaron has been especially devasting given how "no matter what he and I had gone through in our lives, we always were able to make amends, always were able to get back to that place—and now I can't anymore and it hurts."
"It's still unbelievable to me," Nick said of Aaron's death—due to accidental drowning—in an exclusive interview with E! News' Francesca Amiker. "I'm still processing the whole situation and trying to make sense of it—because it hasn't."
The Backstreet Boys star continued tearfully, "But I'm hoping that one day I can make sense of it all."
"My children are my everything," he explained. "If I lost everything—if I wasn't a Backstreet Boy anymore, if I didn't have the opportunity to still perform for people and entertain them—as long as they still had my kids and still had my family, I'd be OK. All this stuff on the outside doesn't matter to me."
In fact, Nick cherishes each and every moment of parenthood no matter how small. As part of his healing journey, he's finding comfort in "trying to be the best father that I can."
"That's what I focus on," the 43-year-old shared. "Being present with my children, listening to them, parent-teacher conferences, driving them to school, taking them to Halloweens and being there when they want to trick-or-treat."
The pop star has also found solace in music. His newly released single "Made for Us" is dedicated to fans who've supported him through thick and thin over the years, with Nick singing in one of the lines, "Always said maybe in another life / Yeah, I could be your love and, baby, you could be mine."
"The reason why I thought that stuck out was I've had so many times where a fan would come up to me and say, 'I want you to know, you were supposed to be my husband,'" Nick noted. "So, here's the song for you. You can have it. This song was made for us."
Nick's song "Made For Us" is out now, with his Who I Am Tour running through November.
Keep reading to look back on Aaron's life in pictures.