The Northwest Justice Project has a nice document on dissolution of domestic partnerships. It is no substitute for hiring a lawyer, but it might be useful to you as you get started. You can find it here: http://www.washingtonlawhelp.org/resource/filing-for-dissolution-of-a-domestic-partners?ref=M3vZj
This advice is for informational and educational purposes, to provide a service to the community. None of this advice is specific to the facts of your case, but is instead a general statement of the law given your limited request for information. Hire an attorney to get legal advice about your particular legal issue. I am not your attorney. Washington state encourages attorneys to assist people seeking help informally. In the event that any jurisdiction believes that this advice constitutes an advertisement, then for your jurisdiction's purposes: this is an advertisement. Though, it is my intention merely to provide general, legal information regarding limited fact patterns.