Here is my take on the conversation you had with your W:

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I think I said I was upset because I have denied myself any spending money for years, and I want to be able to spend my own money and know where my money is going.


It is useless to complain to her. You will get no sympathy. Seeing you hurt only strengthens her hostility.

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W kept asking me why I wanted to close the accounts, and I said I didn't want any joint accounts with her.


Can you close these account unilaterally? If yes, just do it and tell her it is done and there is no point of discussing it. If you cannot, simply do what Steve suggested - get the money out and put it your own account.

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I said I would give her money for food


I probably need to know your past threads more carefully to understand your situation better. But, why are you giving her money for food when she moves out? How long do you plan on feeding her after she moves out?

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She said we were still married.


She is yanking the chain here.

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She said "You haven't signed anything yet have you?"


She is taunting you.

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I told her "You can't have it both ways"


Instead, you should have shown more independence: "I will sign what I see fit, when I see fit."

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She asked if I was accusing her of something.


You should answer: "No." She is taunting you again. She wants you to accuse her of stuff: A, spending, leaving etc. This fuels her "independence". She wants war to justify her her actions. Do NOT give it to her.

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I left the room saying I wasn't going to be yelled at anymore.


Very smart! Good move!

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W tried to make it my responsibility to resume the conversation, but I told her no, she needed to calm down and come to me.


Don't tell her no. Best is not to talk to her while she is yelling. Just listen or leave. Don't reply to a yelling person. Let them yell and appear ridiculous. You can take the initiative to have a conversation only when you find it important, and only when she is capable of having a civilized conversation. This is not something you want to tell her though. Let her see it (multiple times) instead of hear it.

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She protested once more, but I did not engage further.


Awesome! Let her chase you a bit, even if it is just to yell more. You did good.

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Later after she had cooled down she did ask me if we were going to talk any more tonight, and I said no not tonight, I need to go to bed.


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Oh before talking about our accounts she also told me she was moving out in two weeks. Don't know how that's going to work with our son, which is something she wants to talk about.


This is something you certainly want to work out with her. You need to be very cooperative when it comes to the son (unlike the accounts).

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She also told me she found a new gym that costs $100 a month. Not sure why she told me that, but I asked her how she was going to pay for it and she said she'd figure something out.


You did good again. Better not to ask but just state "Nice! Good for you! I hope you can afford it."