What the subject line says, basically. Bucky never tells anyone he was raped in captivity. He figures it's none of their business. But then one of two things happens: either Steve gets captured on a mission and it's painfully obvious to everyone in the rescue party what his captors did to him, or alternately, Steve manages to hide the details of his ordeal from everybody, but Bucky eventually picks up on the clues that Steve is coping badly in the aftermath of a sexual assault. Either way, he's defensive and deeply ashamed, and Bucky winds up exposing his own past to him while trying to get it through Steve's thick skull that he doesn't think any less of him.

+ 1 billion for physical h/c, whether it's cleanup in the immediate aftermath or a more symbolic gesture of Bucky and Steve helping each other wash off.