If you are in a relationship with (or married to) an Australian citizen, permanent resident or an eligible New Zealand citizen, and you would like to remain in Australia -or go into the country- there is a legal pathway you can follow to achieve that.
Spouse immigration is a process which comprises different phases, and each phase is extremely different to one another.
The first thing to realize is that if you apply for this visa, irrespective of whether you are married or in a de facto relationship, you effectively apply for two visas.
The first visa is a temporary spouse visa. The legal language for each sub-type of the visa varies depending on the place where you lodge your application. However, the gaps stop there. The process is almost the exact same. To sum up, this visa lets you remain in the country (or input I), work, research (though you are not able to get government assistance); and ultimately, access Australia's medical health system.
The next visa, or permanent partner visa, essentially grants you the exact items as above, but additionally, you're in a position to apply for Australian citizenship, of course, once you fulfill all the necessary prerequisites to do so.
That's extremely briefly the outline of this procedure. Next point is how to apply for this visa.
When you have done that, you will find two kinds you need to familiarize yourself with: the 47SP (for the applicant), and the 40SP (for the host). Even if you're married and considering another visa, well do not, you still need to complete and lodge both.