You are altering history.
The missiles the USSR was installing in Cuba were not defensive missiles, they were nuclear-capable offensive missiles. This constituted an existential threat to the US.
This was not the situation in regards to Ukraine. Nothing was transferred to Ukraine that could be considered an existential threat to the Russian Federation.
Plus,
Ukraine gave up its nukes in exchange for territorial guarantees. Guarantees that have been ignored.
"After the
dissolution of the Soviet Union, Ukraine held about one third of the Soviet nuclear arsenal, the third largest in the world at the time, as well as significant means of its design and production.
[2] 130
UR-100N intercontinental ballistic missiles (ICBM) with six warheads each, 46
RT-23 Molodets ICBMs with ten warheads apiece, as well as 33
heavy bombers, totaling approximately 1,700 warheads remained on Ukrainian territory.
[3] Formally, these weapons were controlled by the
Commonwealth of Independent States.
[4] In 1994, Ukraine agreed to destroy the weapons, and to join the
Treaty on the Non-Proliferation of Nuclear Weapons (NPT).
[5][6]"
"1. The Russian Federation, the United Kingdom of Great Britain and Northern Ireland and the United States of America reaffirm their commitment to
Ukraine, in accordance with the principles of the Final Act of the Conference on Security and Cooperation in Europe, to respect the independence and sovereignty and the existing borders of Ukraine.
2. The Russian Federation, the United Kingdom of Great Britain and Northern Ireland and the United States of America reaffirm their obligation to refrain from the threat or use of force against the territorial integrity or political independence of Ukraine, and that none of their weapons will ever be used against Ukraine except in self-defence or otherwise in accordance with the Charter of the United Nations.
3. The Russian Federation, the United Kingdom of Great Britain and Northern Ireland and the United States of America reaffirm their commitment to Ukraine, in accordance with the principles of the Final Act of the Conference on Security and Cooperation in Europe, to refrain from
economic coercion designed to subordinate to their own interest the exercise by Ukraine of the rights inherent in its
sovereignty and thus to secure advantages of any kind.
4. The Russian Federation, the United Kingdom of Great Britain and Northern Ireland and the United States of America reaffirm their commitment to seek immediate
United Nations Security Council action to provide assistance to Ukraine, as a non-nuclear-weapon State party to the Treaty on the Non-Proliferation of Nuclear Weapons, if Ukraine should become a victim of an act of aggression or an object of a threat of aggression in which nuclear weapons are used."
Is this what happens when one side unilaterally disarms?