Alexander Pierce liked fucking the asset in front of mirrors, angled so it would have the best views of his cock in its ass.
Now Bucky can't look in a mirror without getting hard, without picturing his face all screwed up and his ass being fucked. It makes him horney as hell and sick to his stomach. The worst part is, he can't get hard otherwise.
Steve notices Bucky's aversion to mirrors, but makes all the wrong assumptions. Thinking Bucky needs a pep talk, Steve marches Bucky over to a mirror to point out somethings, but pretty soon Bucky is grinding back into Steve.