It's usually the first practical question, and it comes up on the first night. She's said it's over, or you have, and somewhere in the next hour one of you says, or thinks, "so who's leaving?"
Here's the short version, and then the longer one.
The short version. In Australia, no, you don't have to move out because the relationship has ended. Being separated doesn't require separate houses; "separated under one roof" is a thing the law recognises. Leaving the house doesn't give up your share of it. Staying doesn't guarantee it either. The one exception is safety: if there's violence, or the threat of it, in either direction, that changes everything and the first call is the police or 1800RESPECT, not a lawyer. And whatever you do in the first week, don't sign anything.
Now the longer one.
Why men leave too fast. I did. Not because anyone made me. Because the house was unbearable, because it felt like the decent thing, because I thought going would make it calmer for the kids. Some of that was true. But I made a decision that shaped the next two years in about forty minutes, with a bag, at night, angry. Most men I've talked to since did a version of the same thing.
Moving out isn't wrong. Moving out on night one, with no plan for where the kids sleep and no idea what it means for the money, usually is.
What moving out doesn't change. Your share of the house, the super, the savings. That's worked out on the whole picture of the marriage, not on who was sleeping where in the last month. The kids' time with you. That's a separate question, decided on what's good for them, and "he moved out" on its own isn't a mark against you. Your right to go back for your things. Your right to a say in what happens to the house.
What moving out does change. The pattern. If you leave and the kids stay, and three months later that's just how it is, then that's the pattern everyone's working from when the real conversations start. Patterns are hard to move. So if you go, be clear from the first week about when the kids are with you, in writing, even if it's a text: "I'll have them Wednesday nights and every second weekend from Friday school pick-up." Not because a text is a legal document. Because it says, from day one, that you're their father and you're not going anywhere.
It also changes the money. Two rents or a rent and a mortgage, on the same income as last month. Do the sum before you do the move, not after.
If you stay. Separate rooms. Separate food, if that's the only way to keep it civil. Write down the date you separated, somewhere you'll find it; it matters later for the divorce timeline and it's the kind of thing two people remember differently. Keep it dull. The goal of a house with two separated people in it is that nothing happens in it worth telling a lawyer about.
If it's not safe. If you're frightened of her, or she's frightened of you, or either of you has put hands on the other, the question of who moves out is not a negotiation. Get yourself and the kids somewhere safe tonight and talk to someone tomorrow. 1800RESPECT (1800 737 732) talks to men as well as women. A man who leaves because it's not safe isn't abandoning the house; he's doing the one sensible thing.
The one rule for the first week. Don't make a decision this week that can't be undone next week. Moving out can be undone. Signing something can't, or not easily. If she, or her brother, or a friend of the family, puts a piece of paper in front of you in the first fortnight, the answer is "I'll have a look at that with someone," and the someone is a lawyer or Legal Aid, not your mate who went through it in 2019.
Where I'd go from here: the what to know before you talk to a lawyer page, and the first-month roadmap. If you're still working out which bit of this you're in, six questions, two minutes.
None of this is legal advice. It's what I'd tell a mate at the kitchen table. For your situation, talk to Legal Aid in your state or a family lawyer; the first conversation is usually short and usually worth it.
Alex