If by Russia, you mean Putin, then Putin is basically sponsoring Yanukovich. From my knowledge Russia and Ukraine had a special multi dollar transaction, after which the Ukraine has decided not to pursue EU membership.
The primary reason is not 15 billions, but trade preferences from Russia. It's 2004 all over again, and Ukraine wants to sit on two chairs - it wants to develop closer ties with the West and doesn't want to lose preferences from Moscow.
I'm not trying to call into question your level of the awareness of this situation but what exactly do you believe a "special multi dollar transaction is"?
Yanukovich sat down with the Euro leaders and couldn't come to an equitable agreement that would help Ukraine in any way. Russia on the other hand offered a $15 billion bailout to help out the Ukrainian economy and a guaranteed low price for natural gas. The elected leader of Ukraine probably thought cooperating with Russia might be a better deal for Ukraine than Euro's offer of asking something for the promise of nothing.
