You can start by looking on Archive of Our Own (AO3). It has a large collection of fanfictions, including ones about Steve and Tony. Just search for the relevant tags and you'll likely find many great stories.
One possible reason could be Steve's strong sense of loyalty to Bucky. Maybe he feels that he owes Bucky so much after all they've been through. He might be so focused on helping Bucky or being there for him that he unconsciously ignores Tony.
The story of Steve King could vary depending on the context. If you're talking about the author, it might involve his journey in the world of writing and the creation of his famous horror novels. If it's about someone else named Steve King, more details would be needed to clarify.