From my experience the third love is the one that endures and understands. I had nothing in common with my first love (high school), I just liked looking at her. I had a lot in common with my second love (Jr year college), but not enough for the relationship to last more than a couple of years. I met my third and final love when I was 25. She left me for a while, then we reunited, then married in our late thirties. We have been married for 35 years. I wrote this sonnet for her recent birthday.

Our love is not a single flash of light

Imprinted once upon our youthful souls

For world enough and time has brought delight

And cast us in a multitude of roles

Love's not a flower to grasp before it fades

But a growing tree eternally renewed

Each moment dies then resurrects remade

A circle changing each time it's reviewed

We are not one, yet each is more than two

Our stories intertwined at branch and root

Our lives a life that each and both pursue

As growth and love give birth to hybrid fruit

As we swim on through fire and through ice

In a river never left, nor stepped in twice