withheld . . . . . . restrained

If there be sorrow 

let it be 

for things undone . . .

undreamed 

    unrealized 

        unattained 

to these add one: 

Love withheld . . . 

. . . restrained 

[Mari Evans {1923-2017} 'If There Be Sorrow', from The Premier Book of Major Poets]