The spouses cease to be responsible for joint debts after separation. Separation is defined as either actual separation or legal separation.
However, if the mortgage was taken out after you were married, you are both responsible (legally) even though your name's not on the loan. If it was taken out before the marriage, it's his separate debt. I think it's a separate debt, since I don't know any banks in WA that will loan to one spouse without getting the other's signature too.
Write the mortgage company and ask them to give you a letter stating that they will not hold you liable for the mortgage. If they refuse, then file for separation or divorce and ask that he be required to refinance the house so that you can't be held responsible in any way.
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This is not legal advice and you are not my client. Double check everything with your own attorney and your state's laws.