Well, the process entails several steps but it really seems to not make any sense for you to do this if your ultimate plan is NOT to live in the US but to move to Australia. A fiance visa is for those foreign nationals who want to immigrate to the US on the basis of their marriage to a US citizen petitioner/fiance. If you do not plan to do that, why would you go through the entire process of getting him a fiance visa? So you can marry in the US and then go back to Australia? Seems like a waste of time and money. If you just want to get married, you can do that anywhere. If he wants to be able to get permanent residence in the US, then do the fiance visa; but if not, I would not bother.
I would be happy to consult with you off forum on the specific situation you are in, as I handle these types of matters for clients nationwide on a daily basis.