Iran has been a strong ally of US till 1975 and since then they have been at the receiving end of the US and Europe. These western powers have been always behind the Iranian government due to perceived terrorism funding by Iran.
These powers have been ensuring that no major foreign company enters Iran for business purpose. All the efforts have resulted in Iran being the only Arab country to still import all Petrol and Diesel needs from other countries. Iran is still unable to exploit the massive gas reserves underneath, due to technology constraints.
Still Iran is no more willing to trust these western powers, and is ready to confront them with force if needed. It is therefore pursuing the nuclear ambitions at the cost of the nation and the millions of Iranians. Once Iran becomes a nuclear power, the Western powers might find a easy way to militarily launch attacks on Iran. Anyway based on current equations, we can expect the wide gap between Iran and the Western powers to continue for decades to come.
Change in this is possible only if the fundamentalist regime is replaced in Iran, which does not look possible as of now.