@engineer,
He said this "She’s at work all day and I’m thinking of just packing up and moving everything and leaving tomorrow while she’s gone."
So yeah one could interpret it to be "sneaking out like a thief." He might have talked to her about it, however, he is thinking of just leaving without discussing it any more.
But like jespah, he can do whatever he wants. Just his comments do sound a bit like a jerk and he did ask for an unbiased opinion. So my opinion is to work it out as amicable as you can rather than sneak out.
I also agree with you in, I cannot imagine wanting my ex's furniture even if it was nice. It's your ex, why would you want anything of his?
And I can understand if there is some underlining reason why you love your furniture; some sort of sentimental reason behind that why you would want to keep it.
There to me, seem to be something that you could both discuss and compromise on. Does she have the means to buy new things for herself? It is tough right now with all the lack of inventory, everything is more expensive and harder to get.