Well, he’s right, and what he should be doing is calling for a meeting of the US, the UK and Russia, who all signed an agreement guaranteeing Ukraine’s borders.
Mind you, I think the best thing might be to divide the country, since a large part of it actually is still Russian identified, particularly the Crimea. But this should be done through treaty and not through force.
I don't disagree with you about dividing the country. But I would be more specific about your statement that "a large part of it is actually Russian identified...".
According to a 2001 Ukraine census 78.1 identify their ethnicity as "Ukrainian" while 17.3 percent identify their ethnicity as Russian.
I think that makes sense.