China never wants to act like your benefactor, since we only seek for win-win.
Iran did make bad decision in the past, and even many of your compatriots do admit that mistake.
For now, no option left for Iran, and China is the only remaining option.
If you can find more capable/reliable partner than China, then go for it. Since everyone has the right to choose the most optimized option for themselves.
And the past, China was also plagued by the pro-west reformists like Iran, and those people were just indoctrinated by those US institutions and they all carried the mission to weaken their motherland in the favor of the west, and eventually opt for a color revolution.
China needs to help Iran to weed out those western stooges fifth columns which will effectively weaken our own traitors.