Eastern  European countries dependency on Russias natural gas would be notable  since the turn of century making Russia a 31% exporter of oil to the  world. After World War II, and the burning of the Baku oil fields in the  early 1900s due to protests, Russia realized by the 1950s that their  mass production of oil, and low price strategies they could be a  dominant force in the suppliers of these resources. During uproar in the  Middle East during the 70s and 80s gas prices began to rise, however,  Russia maintained gas prices at a cost of 50% less than that of its  Middle East counterpart(Goodrich, 2014). Most of central Europe began to  depend on Russia due to the accessibility, contracts with Russia that  allowed for loans on oil exports, and the need for Russia to hold off  western pressures due to sanctions. 
According to Goodrich, 2014:
Energy  revenues make up half of the government’s budget. This capital influx  was and continues to be instrumental in helping Russia build the  military and industrial basis needed to maintain its status as a  regional ” if not global ” power. 
Beyond export revenues, the energy sector has contributed to the creation of a domestically stable and industrialized state. Russia’s domestic energy consumption is very high (Links to an external site.)  due to extremely cold weather for most of the year, but despite  inefficiencies within the energy sector and the cost of producing  energy, the country’s domestic reserves have enabled Moscow to provide  its citizens and the industries that employ them with low energy prices.
This explains why Western Europe and Russia have an indifferent relationship. In fact in 2010 about 34.5% of  Ukraines oil was imported from Russia(Kennedy,2014)  Russia  needs the revenue, and Europe cant get the energy resources at a  better rate. Russia’s physical connectivity with Europe and ability to  undercut any competitors have served as the basis of many of Moscow’s  relationships in Europe(Goodrich, 2014). Moving forward Ukraine and  other Eastern European countries are looking for other ways to bypass  Russian oil imports by getting alternate pipelines, and looking to  innovate other renewable energy sources. In the long run this long  standing relationship if terminated may be harmful not only to the  Russian economy, but also various European nations who cant afford to  get these resources in other places.
References:
Goodrich, L. (2013, February 12).The Past, Present, and Future of Russian Energy Strategy. Statfor Retrieved from https://worldview.stratfor.com (Links to an external site.)
Kennedy, B.(2014, March 4). Ukraine Crisis Highlights Europe’s Dependence on Russian       Energy. CBS News. Retrieved from https://www.cbsnews.com