The mess started with Ukraine basically being forced to choose between economic deal with EU, or economic deal with Russia. Right now, they have a deal with Russia. Problem is that if they also make a deal with EU, it would allow exporters to basically push their EU>Russia exports which are extremely lucrative though Ukraine to avoid tariffs.
A very large part of Russia's budget comes from these tariffs, so Russia explicitly stated that it will not allow for such an obvious loophole, and that if Ukraine does make a deal with EU, current deal with Russia is off.
At the same time, Ukraine is effectively divided along the linguistic lines. About half the country speaks russian, and another half speaks ukrainian. Kiev is in the ukrainian-speaking region, so it's always a mess when a pro-russian speaking government is in power and does something that ukrainian speaking leaders don't like.
There are some other rather nasty issues, like the nature of current protests. Lviv, the home city of the current waves of protests is the home of extreme right movement in Ukraine, borderline nazi movement that wants to purge everyone ranging from russian-speaking minority to jewish and polish minorities. They have about 8% popular support across Ukraine but well in excess of 20% in their hometown of Lviv. They have been a very important power behind mobilizing the current protests, and they also appear to be the ones turning them violent.
Majority of those protesting just want a more EU-like rule. Less corruption, more wealth to the citizens. This is actually one thing that likely unites both the part of the nation protesting and one that is not - they all agree that government is corrupt and want better rule. It's just that pro-Western leaders that were in power for years before showed to be even more corrupt then current leadership, so options are pretty slim.
Also Eastern russian speaking part of the country is calm - it's actually industrialized and manufactures a lot of high tech things such as military helicopter engines for Russia's Mil helicopters. They have a very healthy export economy and they need good relations with Russia - Russia proposed an economic union similar to EU which would bring massive economic boon to that region. This is also why most of the Ukraine's oligarchs who own the heavy industries support the moves to approach Russia, and why they are against the EU deal - they need the current deal with Russia so that their heavy industry exports can continue. In light of the mess in Ukraine, Russia has already made some steps to isolate itself from potential fallout and parts shortage that breaking of their trade agreements with Ukraine would cause, such as laying down a new helicopter engine factory near St. Petersburg. This is very worrying for Ukrainian exporters located in the East for the obvious reasons.
On the other hand Western ukrainian speaking half is mainly agricultural, and of those exports, they want to send as much as possible to EU as it's a very lucrative market. Right now, tariffs keep that trade low, while on Russian market they have to compete with EU companies AND Asian ones. Russian agricultural market is very lucrative, but also extremely competitive and Ukraine doesn't really have the ultra-efficiency of EU competitors, nor extremely cheap labour of the Asian countries. The deal with EU would bring at least some potential prosperity to that part of the country as Ukraine would be able to supply cheap labour-based agricultural products to EU. It's highly unlikely that any of the high-tech exports would be allowed in EU however.
So there you have it. A country split among the linguistic, economic and ideological lines. And split is fairly even, right now it's something around 55% pro West and 45% pro East. No matter who wins in the current political struggle, half of the country will feel it lost. It's a mess. And in addition to that, no matter who it chooses economically, half of the country will likely get economically hit.
On a final note, there's the Ukraine's current economy, which is in shambles. Ukraine desperately needs funds to keep it afloat, and they were allowed to think that if they signed the deal with EU, EU would assist with loans. That was back when they started the negotiations and EU was in a good economic situation. Right now, EU itself is a mess and cannot afford to give out cheap loans - they need them for PIGS (well, minus Ireland which seems to be recovering on the free ride of double irish taxation regime which is a story of its own). So suddenly Ukraine was placed in a situation where it could not receive the loans it needed. Russia on the other hand, keen to push its new economic union model agreed to finance Ukraine with cheap loans. Yanukovitch tried to basically use Russia's offer to try to get money from EU, but it didn't work. So he accepted Russia's offer.
Overall, situation is completely out of control. No one expected it to get that bad, and now it seems that no one really knows what to do about it. I strongly suspect that about the only solution left will soon be use of force to pacify the violent protests, and EU will use a lot of angry words but Yanukovitch will be allowed to pacify the country through use of force - because no one wants Ukraine in grips of some sort of a civil war. It's simply too close to both EU and Russia for either one to allow it to sink that low. And that's where the country seems to be headed right now.