Partner visa paranoia

I’ve been living in Australia on a working holiday visa for 2 and a half years now ( 1st and 2nd year completed, now on 3rd) I am from the uk, my partner is Australian we have been together for 15 months now, and lived together 4 months, obviously the idea of going back to uk terrifies me and I want to stay with her, I’ve looked online about the partner visa and criteria but still have my doubts, does anyone know if my relationship meets the criteria to apply for one? And also what are the general steps? I am aware we have to provide lots of proof / statements which is no issue I’m more so worried about the whole “de facto” side is there a certain length of time we must have lived together etc ? If anyone could help your comments would be really appreciated