What everyone else said plus a bit more.
You need to separate emotion from the business side of this. It is terrible and when it means they left for someone else, pretty devastating. You will need to grieve for the loss of your marriage but you do need to start working on what happens next.
Prepare yourself for your meeting with your lawyer. Don’t waste time on the trauma or emotion of the divorce. Keep it business like. What you need to do is set out what you want and how to get there.
First, the assets you share. House, cars, accounts etc. You need to ask your lawyer about closing/freezing accounts and what happens with assets like the house and a car she might have. If you have access to online banking, go in and print out a statement of all accounts including mortgage, credit cards, loans. Have that set aside. Freeze any accounts she has access to and advise her accordingly. If necessary, set up a new account for your paycheque and expenses on the house. If she has access to the kids’ accounts, freeze that immediately.
Second, start keeping track of monthly expenses for the house. Jot down everything as this will help determine split of expenses.
When you go to the lawyer, outline you want an agreement for child support, section seven expenses and the split of the assets. Even if you aren’t divorcing right away, the assets will need to be split. Do NOT get into a nitty gritty battle as it will simply cost you money on a lawyer. Let her go, don’t look to punish her and keep emotion out. All three of these a the way to lose a lot of money on a lawyer and a waste of energy.
Finally, the biggest question will be spousal. Ask your lawyer what she will be entitled to and what you can argue. If she left you voluntarily for someone else, let them take care of her. You shouldnt be responsible for her ongoing care if she has another income source. Spousal support will be the biggest key in this matter.
I too am sorry this happened and you will get through this. Protect your financial future first and let the rest of it fall into an area outside of the legal stuff.