He thought you were a dream— or a nightmare. Or maybe that’s how he coped with you not being around anymore. He figured you’d lived, like Peggy, had a family and had forgotten all about him. That you’d moved on. Until one day, he finally sees you, and realizes you’re alive. Still physically young. Stuck frozen in time like he is. But you’re working for Hydra now and have no clue who he is. So now he’s willing to throw everything away to get you back.