He still sees her though no one else can. She still goes through the house, making his meals, telling him off for not waking up early enough but she still plants a loving kiss on his cheek. Yes, he sees her. He wants to. Needs to. It’s the only way to make the pain disappear. He makes himself see her. Though she wasn’t really there.
She’s a ghost. A ghost of his past. A memory. That was the only way he could see her.