So, this is not intended as legal advice. But sometimes what we learn in law school is useful and have had me pondering life in the future.
If you want to live with someone, don't. Co-habitating is a bad idea. Why you may ask? I am not talking about moral reasons, I am speaking from purely legal ones. When you split up, the court will not get involved with money owed or with who owns what property. Of course, you can mitigate this by contracting around it, but even then there are pitfalls and problems.
As for marriage, Oregon's property division laws can be pretty harsh. Marital assests and property are to be divided equally. And sometimes even property you owned before the marriage. What I have learned is that I should keep everything seperate and keep meticulous records so that I can prove in court that I never intended to share my property with my spouse. Then maybe I will be able to keep it.