Hi Kiki
Felt the need to reply to this, first and foremost because I'm in the exact same boat, and spend nearly every day weighing up whether to go back or not. There are some huge pro's to Melbourne, the food, the cool bars, the coffee, the outdoor lifestyle, world's most liveable city, the earnings compared to back home (for my profession anyway). Despite all this I just cannot seem to get at and actually live the life that is on offer here. I've struggled to make meaningful friends for 2 years, most of the people I've befriended were travelers that have since gone and it is almost impossible to break into the social groups of the locals (just have nothing in common with the vast majority of aussies). Done so many things to try and meet people that I'd never have considered in the UK; meetups, expat sites, interest groups, heck even online dating(!) but can count my friends here on one hand still, and most of them are married!
It's so frustrating, and as you say its so tough to get any real advice on the subject as most people just think you're living the dream and would be insane to go back. There comes a time, and this will happen for me when you just give up I guess. There's only so much you can do before it's just not worth all the stress and hassle. It'll be a shame if I do leave but if you've given it a good go and left on your terms then that's all you can ask for
I wish you all the best coming to a decision!
Cheers,
Tom