if you do not have a marriage license , you cannot be legally married in Wa. state. Having just a religious ceremony does not qualify as marriage in Wa. -- you must have a license first and than have a religious ceremony if you want to be legally married. The question is simple -- do you want to be legally married or not? If so, you must have a marriage licence. This does not address the issue of whether you want to live together in an intimate committed relationship rather than getting married -- Apples and Oranges.
Please note that THESE COMMENTS ARE NOT INTENDED AS LEGAL ADVICE and are for informational purposes only. This response is not intended to create any attorney-client relationship and is only based on the limited facts given. The response might change should additional facts be learned and should not be relied on as legal advice. It is recommended that you consult with an attorney who can properly assess the situation, as well as all pertinent facts, prior to taking any action based on the foregoing statements
"I give up a lot of my rights as a single woman". I am not sure what rights you would be giving up if you are legally married.
"So I don't understand the benefit to having a marriage license." When the same-sex marriage debate was going on a few months ago, someone made available a list of benefits married persons have. You likely can find the list if you search the archives of Seattle's major newspapers. Some benefits include being able to file taxes jointly, marital privilege against testifying against your spouse in most situations, being considered the spouse's next of kin to make medical decisions if the spouse is unable to make the decisions.
WA does not allow a common law marriage to be formed within its borders. If you do not go through the statutory procedures to obtain a legal marriage, you are not married regardless of what else you do.