Captain America Comics #65

Cap has been seeing a woman named Grace, and when Bucky attempts to take down a member of the crime syndicate by himself and fails, he confronts Cap about it. Cap slaps him, tells him that he's been in his way for too long and dissolves their partnership. Cap ultimately reveals that Grace is the brains behind the crime syndicate and shows Bucky a note that threatened his life if Cap intervened so Cap pretended to be angry with him so he'd go. Now that the crooks are busted, Cap and Bucky are a team once more.