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Washington State recognizes a CIR ( committed intimate relationship) and the courts have the power to divide all assets acquired during the relationship. In a CIR the court has no power to award attorney fees nor alimony. The fact that the 401K is in your name alone does not protect it from claims by your partner. To the extent the 401K was started before the relationship, you would keep the pre-relationship value ( plus its growth). The 401K is tax deferred, so you should deduct 10 -15% of its value ( for the income taxes) when measuring it against the house value, since the house can usually be sold and capital gains tax avoided. After valuation, the assets/debts are divided in an equitable / fair split. Current incomes do not matter when determining the asset split details.
Here is what the initial court papers look like http://www.washingtonlawhelp.org/files/C9D2EA3F-0350-D9AF-ACAE-BF37E9BC9FFA/attachments/3922BA34-A607-0141-DD46-0DA1A1E7BC31/3920en_filing-to-divide-property-and-debts-unmarried-couple.pdf