Iran used to be best friends with Israel. When the Shah a dictator ruled Iran, that was installed after the US couped the democratically elected president. Subsequently that dictator received training for his armed forces and intelligence as well as weapons from Israel. Israel helped the Shah torture, murder and dissappear tens of thousands of people.

Of course after the revolution Iran became hostile to the country that built up the Gestapo in their country. Then the US encouraged Saddam Hussein to invade Iran, killing a million Iranians in the following 8 years.

Iran is right to feel threatened by the US and Israel, since these two threaten Iran since four decades. Still Iran was willing to negotiate and the JCPOA was achieved under Obamas presidency, but subsequently destroyed by Trump to the cheers of Israel. Israel wants Iran to be annihilated since many years, but it wants the US to do the bidding. Still Iran was in negotiations with the US again, that Israel worked hard to sabotage.

It is perfectly rational for Iran to want to develop a nuclear weapon now, as any attempt at diplomacy was met with attacks by Israel.