Where to start? An addict’s beginning of the end? Or end of the beginning?

Hi, how's it going? Welcome! From what you describe, it does sound like addictive behavior, especially if you have trouble quitting it on your own. Ask yourself: what level of support do I need? Do I need to go to a weekly group and see a therapist, do I want to try one first then the other later? Talking this out with someone, maybe an AP (see below) can be helpful in figuring out your needs.

Having said that, I would absolutely recommend trying out a 12-step group. There's little cost to going and you don't have to speak if you don't want to. They vary in nature (some stipulate total sexual abstinence, others let you decide your level of activity), but all are private and confidential, and all are based on the AA's 12-step model. You shouldn't have any trouble finding one in or near Melbourne. Next to Nofap, I've found the group meetings to be the best thing I could've done for myself. Everyone is in the same boat as you, even if they aren't dealing with exactly what you're dealing with. The comradery and support is a major well of strength. The groups I'm aware of are SAA (Sex Addicts Anonymous-- which I go to), SA (Sexaholics Anonymous) and SLA (Sex and Love Addicts Anonymous).

Seeing a therapist independent of the group is good too. Some therapist specialize in addiction behaviors. I don't know what they're called in Australia, but in the U.S. they're licensed as CSAT or Certified Sexual Addiction Therapists. I've found multiple ones in my area through the search function on the Psychology Today website (there has to be an Aussie equivalent). But don't worry too much if you aren't able to book a CSAT as most therapists are trained in dealing with addiction in some form.

As for day-to-day help, finding an AP (Accountability Partner) and keeping a journal here can help in processing your thoughts. AP's are valuable resources as they can help you with your blindspots through the recovery process. I don't know too much about technology locks and all that stuff, I'll leave that to someone else, but if you think you need it, its probably worth getting.

Give yourself a pat on the back for coming here though. You're right, its really only a matter of time before something like this gets worse, and its best to nip it in the bud for you and your family. The good news is, if you commit to the program (12-step) things will get better. I've seen major progress in people. There is a dawn. God bless. Hit me up if you want any further info.