The correct answer to this open question is the following.
Although you do not specify what is the name of the poem -because the author wrote many- we can comment on the following.
The idea St. Vincent Millay is trying to form about the suffering of both the missing men and the abandoned women at home is an idea of sadness, remorse, and loneliness.
Yes, we are referring to his "Sonet 29." In This poem, Vincent Millay expresses feelings of bitter loneliness and nostalgia for the things he remembers from past events.
Millay writes that is the mind the one that thinks but is the heart the one that feels. And the heart is what produces those sentiments of sadness for the things that are gone and never will be back.