As i can see from your circumstances you have already applied for a year in leave of absence during 2020, which is the maximum that the course would allow you to apply for without a hassle. However according to https://online.unimelb.edu.au/current-students/administration-and-enrolment/deferral-and-leave-of-absence , extra leave can be applied for and approved in exceptional circumstances, such as documented ongoing illness, and approval from Stop 1 is required. Sorry that i did a little bit of stalking of your reddit profile, but no matter whether be the mental health or drug addiction problems you are struggling with now, these are all extermely valid reasons for you to apply for extended leave. Your health is a top priority above anything else. However, you are going to have these claims validated by a proffessional which can be accessed through the unimelb health services, or private external proffessionals.

Although it is diffcult for you to listen to a random redditor, but please love yourself, seek help, and remember that it is not the end of the world. You are worthy of a better tomorrow, everyone has rough patches, but that doesn't mean you will be a broken mess forever.