I hope that counted as 'loss'. It's Severus looking back on him losing Lily, and him losing all these chances to say these things that he'll never be able to again.
Severus had failed to say many things. When they were children, he had never whispered, “You're everything to me.” When they were teens, he had failed to say what could save their friendship. When he was a man, so aware of his feelings, he had never said, “I love you.”
Words were empty and void. If he had told her he loved her, she would never have understood how much. That was why, even as he stood on her grave, he couldn't speak what his heart so often screamed. Because somehow 'I miss you' didn't quite say it.