Russia neither used nor threatened to use nuclear weapons against Ukraine, so there was no violation of the Budapest Memorandum. At the same time Ukraine reaffirmed in a separate statement its commitment not to stir up anti-Russian, neo-Nazi and xenophobic sentiments. What happened after Maidan was a flagrant violation of these obligations by our Ukrainian neighbours.
The Budapest Memorandum states that "The United States of America, the Russian Federation, and the United Kingdom of Great Britain and Northern Ireland, reaffirm their commitment to Ukraine, in accordance with the principles of the CSCE [Commission on Security and Cooperation in Europe] Final Act, to respect the Independence and Sovereignty and the existing borders of Ukraine". https://www.larouchepub.com/eiw/public/2014/eirv41n08-20140221/34-35_4108.pdf, https://sut.am/en/archives/2396, https://euvsdisinfo.eu/report/russia-has-never-violated-the-budapest-memorandum-because-russia-promised/. This was clearly violated by Russia https://eeas.europa.eu/headquarters/headQuarters-homepage/37464/eu-non-recognition-policy-crimea-and-sevastopol-fact-sheet_en.