Bucky and Steve are captured by some Hydra goons, who restrain them both and then commence a trash party with Bucky. But every time Bucky comes, they torture Steve in some way (I’ll love you forever if whatever they do to Steve is completely non sexual or just incidentally sexual; their primary objective is to cause pain). They’re very up front with this. Bucky comes, Steve gets hurt, Bucky watches. Then they force him to come repeatedly until he physically can’t anymore (after all, they’ve got 70 years of trash party records to review, so they know exactly what takes him to the edge).