The only time Steve knew when to stop at this point was when Bucky told him to. He wasn't adept at paying attention the strength of blood flow or the speed of Bucky's heartbeat. When he wasn't feeding, sure, he could tell. But he completely blocked everything else out, except for what was directly affecting him, like Bucky's hand in his hair.

He groaned against Bucky's leg, sucking sharply in response. Nails scraping his scalp only encouraged him more. Blood flooded his mouth and he swallowed it all down with a gulp. Meanwhile, his thumb rubbed circles into the tip of Bucky's cock. It was just too bad that only a little bit of attention was out into that. If his focused stayed as it was, his hand would likely stop movement altogether. Sorry, Bucky.