They made a deal way back that the US would keep House of Saud in power, in exchange for their Oil at market prices. That - and the fact that they are allies on 'terrorism' means a degree of mutually beneficial transactions.
Strategic partners, that's it.
The US does things that massively piss of the Saudis - particularly the removal of Iran sanctions. That is pretty much #1 worst thing that the US could do, outside of withdrawing support for them unilaterally.