"We just got in after so much effort and now it starts to fall apart." My Bulgarian friend, who uttered these bitter words, is not alone. The sense of disappointment about the Brexit referendum is shared by many in the EU's eastern half.

The regular scaremongering about Eastern European immigrants during the Brexit campaign and the realization that the referendum comes at a time of profound crisis for the EU have worried Eastern Europeans even further. As a result, there has been a small but intense Brexit fever in Eastern Europe.

This response should come as no surprise. For Eastern Europeans, EU membership is more than visa-free travel and European funds for development. It is the bedrock of their post-Cold War identity, as it stands for two things.

The first is the region's success in building democratic, market-oriented societies out of the terrifying instability and poverty that followed the fall of the Berlin Wall. The long, hard struggle of Eastern European countries to build such societies with the invaluable support of their Western partners culminated with their accession to the EU. EU membership also represents the recognition that, in spite of decades of division and underdevelopment, Eastern European countries are part of Europe.

A Brexit would be a crippling symbolic blow to this EU-centered identity. It would raise some fundamental questions. Would the international framework which has fostered the transformation of Eastern Europe in the last generation persist? Would the erection of new borders leave the EU's eastern half as a second-class Europe, again? Have Western Europeans started to see Eastern Europe as a burden?

Tough questions, behind which lurks the toughest: what would happen with the EU? If the UK leaves the union, this might usher demands for further referenda and result in other countries leaving the EU. The likelihood of such a scenario is small but the EU is vulnerable. Faced with economic slowdown, a rift between the North and the South and an ongoing immigration crisis which has unleashed a huge domestic backlash, the EU sees its very raison d'être increasingly questioned. Even if a Brexit does not kick off more referenda, it would shake Europe and set up a dangerous precedent. For Eastern Europeans this raises the nightmarish possibility that their promised land, for which they fought so hard, might just be a slow sinking Atlantis.

Beyond these big picture issues, UK's referendum would face EU's eastern members with more immediate challenges. Two stand out. The referendum would inevitably weaken both the EU and NATO at a moment when Europe faces unprecedented external challenges.

The war in Ukraine and the dramatic deterioration of relations between the West and Russia present Eastern European countries with a severely worsened security environment. The ongoing refugee crisis has also caused fierce political infighting, domestic backlash, and Turkey's attempts to use the refugees as a bargaining chip. These external challenges demand unity, clear strategic focus, and an active policy by Europe and NATO. Brexit, which would generate a large crisis in the EU and could potentially destabilize NATO would make all this much more difficult.

A Brexit would give Eurosceptic forces throughout Europe a major boost. The debate around the referendum has also featured regular attacks on the migration of Eastern Europeans to Western Europe.

Everybody in the union would suffer from the consequences of a Brexit, not least the Britons themselves. The UK would see its international clout diminished, its economy affected, and its unity challenged by renewed calls for Scottish independence.

However, the biggest losers would be the weakest and poorest members of the European family, the Eastern Europeans. On a practical level, Eastern European countries would suffer from the destabilization and weakening of the union that a Brexit would wreck, while on symbolic level, a Brexit would be a giant blow to their EU-centered identity and everything that it stands for.

More important, it might also be the first step in a process of European disintegration. Such an event, unlikely but no longer unimaginable, would be a disaster. Eastern Europeans would be again in the uncertain, harsh world outside the EU's ruined house.

The author is a PhD student at King's College London (KCL) and an advisor to an MP at Bulgaria's National Assembly. opinion@globaltimes.com.cn Follow us on Twitter @GTopinion