All the canon to me. ALL THE CANON. He doesn't go back because he doesn't want to disappoint Steve. Natasha defecting to keep him from getting repurposed. When he comes back into the field of work, sitting in the monitoring room, eating takeout and monitoring what happened to Natasha, left behind. Coulson's smile of pity for Steve, and I still can't get over how much I enjoy Steve and Bucky, going sixteen rounds until the paralyzers.

HOW DID I DEVELOP HEADCANON FOR FUCKING BUCKY BARNES AND SEBASTIAN STAN.