Many Turns and Doublings

We've been through a lot, you and I.
Ups and downs, twists and turns,
blinking in and out of each other's lives
like flicking a light switch on or off.
But nothing has broken the bond we share,
nor will anything break it.
The good, the bad, the shades of gray,
I wouldn't give any of it up for the world.
And no matter what happens in this ever-changing life,
I want to be your constant.