This may be all you really want, but you're asking for something in addition to these. You're asking to be able to do these things in the United States, which means dealing with US immigration laws. The US government requires a guarantee that you won't become a burden on the taxpayers at least until you've contributed enough to the national treasury to have earned that privilege. This guarantee has to be provided by someone who is subject to US law (a US citizen or permanent resident), and who has sufficient income and/or assets to back up that guarantee. They do take into consideration your ability to support yourself - your job history, your age, your health, your education, etc. But they still require that guarantee.
When two Americans marry each other they don't have to prove financial sufficiency to the US government, just as your friends don't have to. This has nothing to do with marriage, and everything to do with immigration. Every family based immigrant requires a sponsor - parents, children, and siblings - not only spouses. Don't take it personally. The US government isn't questioning your integrity or your intention to support yourself. They're only protecting the taxpayers from having to pick up the tab for immigrants.