Marriage is the product of how many generations worth of experimenting with social contracts? You have to be either very young or lack a healthy dose of humility to think you can come up with a better system (in general, not just your case). Or, as I suspect, it's just rationalizing for not being able to build a strong, healthy, life-time relationship. I am in that category myself, as are many people of my generation from where I come from. But I don't need to fool myself I found something that works better.
Even just in theory: a friend simply does not take on the responsibility of taking care of you. He is not invested in your household's success. And I could go on but arguing theory is mostly pointless. Even if your arguments against sound perfectly logic you're missing something for sure. Because in practice marriage is just like democracy: the worst system except all the others. It has stood the test of time in practice.
And if your partner tells you that you're not number 1, that's not really your partner. Run. Now.