See this is the issue. When looking at the support of terrorist organizations, you need to look at it from both sides.
America and NATO have waged wars in basically every neighbour of Iran except a few. They've been directly helping Saudi Arabia with selling them a crazy amount of weapons. Saudi Arabia is a state that has many times threatened Iran.
All these support for different factions are a geopolitical game. Criticizing Iran for playing the game doesn't make sense as the second they stop their statehood is threatened.
I just would like to add that I hope they stop, but I know why they don't.
Now about the nuclear weapons. This is simply not the case anymore. Let's tackle what you said about that one by one.
- Iran is developing nuclear weapons. - No they aren't. The agreement they made with 5+1 clearly puts Iran under a magnifying glass of scrutiny. The EU and the white house have said countless times that Iran is keeping their side of the deal up.
- Threatening Israel. - This is true, however, Israel is the only country that hasn't signed the NPT. Yes they can technically make nuclear weapons now since they haven't committed to not making it, but at the same time saying Iran threatens them is an understatement. There have been dozens of Israeli officials that have threatened Iran with war. AIPAC has been seriously lobbying in the US to go to war with Iran. So it's not one sided, it's not like Israel is this shining rainbow and Iran is the evil fire nation.
Let's stop looking at stuff in black and white.