I went through pretty much this exact scenario in 2003. I am going to give you some general advise based upon my personal experience; take from it what you wish.
1. Reconcile if possible. If you love her and there is any possibility that the marriage can be salvaged then try that before any of the other options.
2. If can't be salvaged then you must do everything you can to protect your interests. Your natural inclination will be to give her everything and make her life as easy as possible for your child. Don't do that. You need to protect your interests because you need to rebuild your life and you'll have enough emotional baggage for a while as it is, without financial baggage as well.
So...
3. If the house is jointly owned, DO NOT move out. Under any circumstances. Insist that it is sold and split any equity equally between you. Do not leave the house until it's sold and contracts are exchanged. If you're renting then you can ignore this paragraph entirely.
4. Calculate 15% of your net salary. This is the amount the CSA will require you to pay for one child. Do not pay this to her until such time as you have both left the house and do not give her a penny more. You can obviously treat your child as you see fit (clothes, trips etc.) and contribute to school outings if appropriate.
5. If you have any debts in your name (excluding the mortgage) that you assumed for the betterment of your family's life and you have savings, then use whatever savings you have to pay that off. Don't discuss with your wife, just do it. Otherwise, she'll get half of any cash and you'll be left with the debt. Wise up. This part is super important to your future.
6. Agree a reasonable pattern of childcare. If you fight over childcare in Court, unless your circumstances are exceptional you are most likely to be awarded alternate weekends and half of all holidays. Christmas to alternate. Suggest that to start with and have it detailed in any subsequent Divorce agreement.
7. Regardless of the reason for her decision, regardless of how you feel, regardless of whether she provokes you, you must never lose your temper with your wife. Especially in front of your child. You must never bad mouth your wife to or in front of your child. You must never use your child as a weapon or source of intelligence. From this point on, you must become Mr Reasonable but Firm. You will thank me for this when it gets to Court.
8. Constant reassurance for the child. They will want to know why you left, it's OK to say that Mummy and Daddy don't love each other any more, but that you love the child very much. Constantly reinforce this because it is going to be very difficult period for them.
9. Don't be surprised if your wife turns into a Harpy during divorce proceedings. Legal advice by its nature is adversarial - because it makes more money for them.
There's loads more I could say, but that's a start.
Oh, and I realise that you feel your World has ended, but really it hasn't. There is life for you after this. I happily remarried and have gone on to have three boys. Just give yourself time to work through all of this and keep a sense of perspective. Your child still loves you, it doesn't matter if your wife doesn't.
Keep calm and good luck.
