Great Britain is not a country. The United Kingdom is planning to leave. And as you clearly didn't read what I said last time you asked the same thing, here it is again.
It will leave, as It has given notice to leave over 2 years ago as prescribed in Article 50 of the Treaty on European Union and is only still in because the EU has agreed to extend the time. Twice. The only question is on what terms. And if the House of Commons doesn't get its act together and agree to some, the UK will just fall out with nothing agreed when the EU gets fed up with more extensions of time.
The only way of stopping this is for the UK to withdraw the notice. Article 50 says nothing about this but the European Court of Justice says it can, so it is possible. As this would be an obvious rejection of the referendum result, this British voter, for one, will conclude that it is never worth voting again. Why bother, when politicians ignore us?