Up until last month, Kerry Bloch and her husband, Robert, had never really heard their son speak.

David arrived in their lives 21 years ago after doctors told Kerry she’d never be able to have a child. When she gave birth to him at age 40, she proved them wrong.

But at around 4, David began showing signs of severe autism.

“He was fine and then he just kind of lost it all,” she told BuzzFeed News.

David stopped speaking, and to this day only talks in single words when prompted. He can go days without saying a word, Kerry said.

“My husband and I, we don’t really know what happened,” she said of his autism, “and honestly we don’t care what happened. It’s water under the bridge and we’re just moving forward and trying to give him the best life possible. That’s all that matters.”

David also developed a severe immunodeficiency disorder that meant he needed to be isolated from other kids in their Neptune Beach, Florida, home in order to prevent him from getting infected. Kerry takes care of him full-time, calling David her best friend.

Still, she knows her son is lonely — and it breaks her heart. David sees people on TV laughing and hanging out together and wonders why that can’t be him.

“He wants friends badly. He’s home-schooled, and it’s just the three of us,” she said. “I know he’s lonely and he wants friends.”