(NBC) -- A.J. Boik was the life of the party. He was only 18 years old, but he changed so many lives. His close friends say he was really good at pool. He played viola.
He was really outgoing and always fun to be around.
Alexander Jonathan Boik - or A.J. as his friends and family called him - was the guy you would have wanted to know.
His friends say he was always helping people and brought everyone together.
It never mattered which group of friends you were a part of, Boik was the guy who was friends with everyone.
He was also Lasamoa Cross' first love.
"My favorite memory was when he told me he loved me on his back porch," Cross said. "We promised we'd be together forever. We had planned on building a vineyard in the mountains."
The couple met in 2011 while on a concert band trip to South Dakota.
Lasamoa says she was going through a break up and Boik was there to listen.
She says ever since, Boik was the rock in her life, the one person she could always depend on.
"We would do everything together," she said. "We were together every day. We also went to the movies every week over the summer."
On July 20, Cross and Boik went to see the "Dark Knight Rises" in Theater 9.
Cross says when the gunman first walked in, she thought it was a prank.
After people in the theater started leaving, she and Boik knew something wasn't right.
"He grabbed my hand and was like, 'babe we gotta go'" she said. "I looked back and it looked like he had fainted, and so I panicked and threw my body over him. But it was too late. I don't even think I've clicked with reality."
But the 18-year-old left behind little gifts without even knowing it.
He made life a little bit brighter for those who knew him.
"Each one of my friends, I see a little bit of A.J in them, because he changed them that much," Cross said.
And for his girlfriend, AJ left behind a deeper mark.
His personality and the love they shared changed her life forever.