How does Washington state law work for the timing of counter-offer and offer withdrawl on a property purchase?

I was in the process of purchasing a condo in Seattle, WA and submitted an offer for the property. They were not happy with the offer we provided, but we were able to negotiate and obtained a verbal agreement to terms. I was afterwards emailed a written counter offer, which I signed and emailed to my realtor. Then 10 minutes later my agent emails me to inform me that the counter-offer that was proposed has been withdrawn by the sellers, as they have received another offer that is higher then ours. At this point is it a binding contract, or has it been successfully withdrawn based on the laws surrounding property purchases in Washington state? Up until what point is the seller able to withdraw there counter offer? Are they able to withdraw after I submitted the signed papers to my agent?