Bucky is genuinely not that upset about the occasional sexual abuse he dealt with during the Winter Soldier years. A lot of it was dubcon--out on missions in the middle of nowhere, teammates who hadn't been laid for months, blowing-off-steam sex that was just a few shades darker and more coercive than the furtive handjobs he and Steve exchanged in their tent in the 40s. A lot of the other instances, mostly superiors taking advantage of the brainwashing, he barely even remembers. He jokes about it sometimes, and is still good at the "put up and shut up" approach to sex he doesn't enjoy, but he's way more fucked-up about having been forced to kill for Hydra than he ever was about occasional forced blowjobs.

Steve was violently raped by the enemy after being taken prisoner. Just once. He can't bring himself to talk about it. He's fine having sex with Bucky--that's different. But some things--the slightest hint of degradation, biting at a particular spot on his neck, dirty talk while he's getting fucked--make him suddenly tense up and turn to ice. Made worse by embarrassment, for freezing up over a single instance of something Bucky dealt with for years.

Naturally, their sex life is fantastic, if by "fantastic" you mean an unholy mess of issues.