Legal Question in Family Law in Washington

Re: common law marriage

Not if they live together the whole time in WA since a common law marriage is not formed within the borders of WA.

However, WA courts recognize the doctrine of meretricious relationship. Under that doctrine, members of a couple who live together like a husband and wife and meet other requirements have rights in the properties that would have been community properties had they been married with each other.

Your son and his girlfriend may want to review their facts and options with separate attorneys if they cannot agree with each other.