Prior to the legalization of same-sex marriage, Oregon put in place the domestic partnership option. The ability to legalize your relationship provided many benefits, but it was not the same as a marriage.
The state explains a domestic partnership is only available to two same-sex partners, which is different from marriage, which is available to same-sex or opposite-sex couples.
Another important distinction is Oregon does not recognize domestic partnerships from other states. Other states may also not recognize the domestic partnership from Oregon. With marriage, all states recognize marriages from other states as long as they occurred legally.
One of the main benefits of a domestic partnership is it allows you to act as a married couple for state and local taxation. You can get the tax breaks that come with being able to file as a couple. But the federal government does not recognize domestic partnerships for tax purposes, which is different from marriage, which the IRS does count.
This difference between marriage and domestic partnership is the most complex. Because you will usually use your federal tax returns to file state and local paperwork. But you cannot do that in this case. That means you will need to do your federal taxes two times. One is where you file as single as required by the law, and that is the one you will turn in to the IRS. The second filing will be for your information only, and you will not file it with the IRS.
Whether you marry or enter into a domestic partnership is your choice. But it can be helpful to consider the differences and how your choice may impact you.