Grief

Tony felt his knuckles bash against the hardwood door. A number was etched on it, but he hardly noticed it. He felt empty.

When Thor had beamed him back through the Bifrost after the war, everyone had hoped that Tony would have known something, anything really, that could help them. But not a single word had left his lips. His voice was still in Titan, screaming for his child to come back.
Lost in his own mind and drowning in his guilt, Tony didn't eat or sleep. It was almost every night that Pepper had fallen asleep embracing him, warming his cold skin with hers. A week had gone by in the blink of an eye, and Tony felt his heart drop as a single name flashed before his eyes. May. He had to talk to her. He had to beg for her forgiveness.

Here he stood, waiting in a hallway of an apartment building in the midst of Queens. His knocking echoed in his ears. "Peter? Is that you?" A hopeful voice called out from behind the door. Tony couldn't answer. The voice was followed by the fast pattering of bare feet against wood floor.

"Thank god. I have been so..." Her voice drowned out as May Parker slammed open the door. Her face lit up as she saw Tony Stark, the man who had been like a father to her Peter. She looked around trying to spot her boy, the child she'd sworn to protect at all costs. She nearly had a heart attack when she found out about the other part of his life, but Tony Stark had been there to help Peter train and become his best self. Somehow they had convinced her to let him keep running around on the streets, but of course he had a curfew. "Peter?" Her face shifted from hope to sorrow the second she looked into Tony's eyes.

Tony had planned out a speech. He was going to tell May what had happened, that there was still hope and that he would do anything he could, heck, even more than that, to get Peter back. But when he saw the confused sadness in her face, he broke. Tony felt dizzy and zoned out. He nearly fell to the floor, being saved only by the arms of May. Her voice was overflowing with panic. "Where is Peter? He should be with you." She talked faster and faster, her pitch raising with every word. "You told me you'd keep him safe, you promised me. Why isn't he here? YOU PROMISED ME!"
Tony's face was wet with tears. He leaned in, close to her ears. His voice was dripping with guilt when whispered a single sentence. "I killed him."
May wanted to push him away. She wanted to hurt him. But she looked down at the broken down man in front of her and somehow she understood. She pulled him close and hugged him tight. There they stood for a long time, drenching each other's clothes in tears. The broken hero and the lonely woman, both grieving the death of their only child.