More than just this treaty with the US and UK, Ukraine has an agreement with NATO as well. Given that they had started the MAP (membership application process), all Ukraine has to do is make a request to NATO for assistance, even though they are not an actual member of NATO.
In 2002 NATO and Ukraine signed and adopted the Ukraine Action Plan. Russia's reaction to this was violent. In 2010, when the recently deposed pro-Russian President of Ukraine was elected, he and the Ukrainian parliament stopped the NATO MAP, but did not withdraw completely, so technically, the MAP is still in place.
Add to this; that Georgia is also involved in a NATO MAP, that the Russians invaded Georgia in 2008 and GW Bush had to send the 6th Fleet to the Black Sea to impose a no-fly zone over Georgia, what Georgia may do regarding requests for protection from potential spill over in this event may lead to NATO forces entering the Black Sea... and, dozens of other players such as Moldova and Romania which also have treaties with the US and UK... And lastly... Turkey which is just across the Black Sea from all this tension, is and has been for decades, a NATO member country.
What worries me are as follows: the White House just made the announcement to reduce our military force to pre-WWII numbers; the White House put a "line" to not be crossed in Syria and did nothing when the line was crossed; the White House has allowed Russia to take over and lead Iranian nuclear negotiation; the White House bowed to Russia in relation to force in Libya and and other Middle East conflicts; the White House has bowed to Russia and removed our missile defense systems from former Soviet block regions; Vladimir Putin has stated numerous times that he wants to reform the Soviet Union and is doing everything he can do to consolidate his power and gain territorial dominance, and; now the White House is attempting to draw another line in regard to Russia which Putin is obviously laughing at in the face of the world.
In essence, I don't feel comfortable at all that the White House has the talent, knowledge, vision or most importantly the respect of other global leaders to control this situation before it grows and gets completely out of control.
This rings close to what those that study history will remember occurred in the Sudetenland and even Austria in the 1930's.
History repeating itself.