Romeo continues to reflect on the double meaning of the word “sadness.”

sadness = unhappiness 

sadness =  seriousness

He notes that one may urge a sick man to make out his will in sadness, in all seriousness, since it’s important that this task gets done before he dies.

A sick man, in sadness [in all seriousness], makes his will

But Romeo thinks that “in sadness” is a poor choice of words to use when urging someone like himself to do something seriously since his illness is one of sadness.  The last thing he wants is to be reminded of his broken heart.

As he puts it, sadness is “ a word ill-urged to one that is so ill.” 

A word ill-urged to one that is so [in this manner] ill

Eventually, Romeo does respond to Benvolio’s urging, using seriousness in both its meanings:

In sadness, cousin, I do love a woman.

In sadness [in all seriousness] cousin, I  do [sadly] love a woman.