The Avengers

You and Steve were good partners, until one day, a mission went wrong. The team was infiltrating a HYDRA base, unaware that the building was rigged to explode. You were trapped under the rubble while trying to escape with Tony and Nat, and they ultimately had to abandon the building without you, telling Steve that you didn't make it. Steve was inconsolable, obviously. He mourned you, and it took him a long time to try to move on with his life without you. But you didn't die. Years passed, and Steve eventually moved on and even got a girlfriend, Lilly. You were a sensitive subject between Steve and Lilly. She would get jealous over little things, like discovering that Steve still kept a picture of you in his wallet, or when he visited your gravestone, which he had made for you. Meanwhile, you were currently a prisoner of Hydra.