Fidelity and love are two different things, like a flower and a gem.
And love, like a flower, will fade, will change into something else
or it would not be flowery.

 ... 

And man and woman are like the earth, that brings forth flowers
in summer, and love, but underneath is rock.
Older than flowers, older than ferns,  ... 
older than plasm altogether is the soul of a man underneath.

And when, throughout all the wild orgasms of love
slowly a gem forms, in the ancient, once-more-molten rocks
of two human hearts,  ...  a man's heart and a woman's,
that is the crystal of peace, the slow hard jewel of trust,
the sapphire of fidelity.

The gem of mutual peace emerging from the wild chaos of love.