Romeo is of the mistaken belief that Juliet has killed herself. Utterly crestfallen at the news of what he believes to be his beloved's death, he resolves to follow suit and commit suicide.
To that end, he visits an apothecary in the hope of buying poison. When Romeo arrives at the shop, it's clear that the apothecary has seen better days. His business is floundering and his physical condition is truly wretched. A “meagre”, “needy” wretch, the apothecary is aptly described by Romeo as having famine in his cheeks and “Need and oppression” starving his eyes.
To some extent, the apothecary's drawn, haggard appearance foreshadows Romeo's death. His sole intent in visiting the apothecary is to buy some poison with which he intends to kill himself and join his beloved Juliet in eternity.
In the event, the apothecary agrees to sell Romeo what he wants. Under the circumstances, that's not altogether surprising. The truth is, he desperately needs the money. That's what he means when he says that his poverty but not his will consents. He knows that the poison he sells is deadly, but he's so dirt poor that he has no alternative. And so Romeo leaves the apothecary with what he came for.