I would agree with Don that you need to talk with a lawyer. I'm not really sure what you mean by a guest, but a lawyer is the person you should discuss that with, rather than strangers on the Internet. And in this case you might need a family law lawyer rather than a real estate lawyer.
Assuming you mean that you and with "guest" are or have been in some sort of romantic relationship, there may in fact be some concern there. I don't remember Washington's current case law regarding "meretricious relationships."
As to what samiejohand said, title to the property being in a certain name will not necessarily control ownership (although it might affect right to possession in some instances). Both with community property of married couples and meretricious relationships the title could be in one of the parties with the other party making a claim to part of the property.
Disclaimer: This answer is not intended to be legal advice, but instead suggests that "Nasif" contact an attorney and obtain proper legal advice after disclosing all of the relevant facts.