Nations do not have friends. They only have interests.
What I have proposed is a good imperial solution. But since the US is an anti-imperial institution, it is structurally incapable of doing what is necessary. Therefore, the best option at this point is for the troops to withdraw to Kuwait and Qatar and let the Shia and Sunnis sort things out for themselves.
"Nations do not have friends. They only have interests."
People have friends. And nations are merely collections of people.
Loving thy neighbor is the duty of all humans. A duty we fall short of, generally.
That said, looking at it from what is apparently your self-interest-only-here-and-now point of you, it is the USA's interest to be a bed-rock solid, reliable, friend.
Cut-and-run and no one would EVER stick their neck out for us.