Sure, you can forego a legal state recognized marriage, and then get a lawyer and draw up a detailed contract that specified how a couple of people want to live together, but even then ... there are things that no contract you draw up can secure for you, that a legal state marriage can.
There are going to be holes in whatever you draw up.
We’ll agree to disagree, I guess...
There are loop holes only if someone wants there to be loop holes...