When he prayed about what to say, Southers said, he was reminded of Job, the Old Testament figure who lost his possessions, his health and his family but kept his faith.
Mills, who moved with Amos and their son into a Rosedale apartment in June, met her in 2007, when he was a football star at Kenwood and she was on the volleyball team.
He told the crowd, which filled the pews of the church and spilled into the lobby, that his time with Amos had been the best five years of his life.
"We used to have this argument, once a week or so, about which one of us was more popular," he said with a smile. "I'd tell her, 'Girl, come on, I was the football quarterback!' But I look around at this crowd today, and I see it wasn't even close."
Mills said he had been planning to propose to Amos at Kenwood High School and marry her sometime next year. Turning to Amos' mother, Alisa Grinage, and other members of her family in the first two rows, he asked for their continued love and support, especially when it comes to raising Geron II, who sat in his lap for much of the service.
"[LaRelle] left me with our most prized possession — our son," he said. "Please keep me and him in your prayers."
The Rev. Bishop Moore, Amos' longtime music teacher at Stemmers Run Middle School, described her as an individual who always reached out to new students and who was a gifted peacemaker when peers had disagreements.
Though Amos was killed on an especially bloody weekend in Baltimore, few at the funeral seemed to see her death as signifying anything unique about the area. They saw larger implications.
"It's the state of what's going on, the times right now," said Moore. "First there was [the massacre at] Columbine. Now it's happening everywhere. Who'd have expected the shooting at Perry Hall [High School]? It's hitting everyone."
The Rev. Dr. William Gray III, pastor of St. Stephens AME, who presided over the service, said tragedies like Amos' death are less endemic to Baltimore in particular than they are the result of a general societal decline in young people's understanding of right and wrong.
"It used to be that they learned their values within the family or in church. Now, too many are learning them in the street," he said. "They've learned to 'satisfy myself.' If someone hurts their feelings, so many will kill without a second thought. This is one selfish world."
It has struck him and his colleagues in ministry, Gray said, that as many young people as older ones appear to be dying today — "and that is a complete and total change," he said.
When the service ended, Mills greeted long lines of well-wishers as he stood beside the hearse that would take Amos to her final resting place, Most Holy Redeemer Cemetery in Baltimore. Many hugged him, clapped him on the back or shared a brief prayer.
Mills said he has stayed in touch with detectives but has been told there are no new developments in the investigation since last week, when police asked the public to share any relevant information.
His son, he said, is doing well, but he believes young Geron senses that something is amiss in his family.
"It's important to keep this case alive and out there," he said, tears in his eyes.
Baltimore Sun reporter Justin Fenton contributed to this report.