Here the irony is not that the poem advocates suicide but says the opposite. The irony lies in indirection, as it offers unexpected and ultimately despairing reasons for avoiding suicide and continuing to live, and in the ambiguity of the title: the word resume, without accents, means to "go on again, after an interruption; to continue," all of which is appropriate to the poem. Resume, with accents, means a "summary," particularly "a brief account of personal qualifications and experience," as if the poem summarizes the speaker's experiences and qualifications in this area (the speaker has tried them all and knows!). Irony can entail humor -- as in the title and development of this poem; often there is a serious edge to or point behind the humor.