What plans does Romeo make when he learns Juliet is dead?

In act five, scene one, Romeo's servant, Balthasar, informs him of Juliet's tragic death and mentions that her body lies in the Capulet tomb. Romeo is astonished and disheartened to hear the news of Juliet's death and immediately instructs Balthasar to bring him some ink and paper. He then tells his servant that he will return to Verona that night. Once Balthasar exits the scene, Romeo discusses his plans for the evening by saying,

"Well, Juliet, I will lie with thee tonight" (Shakespeare, 5.1.36).

Romeo then recalls seeing a poor pharmacist, who he believes would sell him some sort of poison. Romeo then visits the local pharmacist, where he purchases the poison before returning to Verona and traveling to the Capulet tomb where Juliet is buried. Romeo's comment about lying with Juliet and his purchase of poison implies his plans to commit suicide before the end of the play. In act five, scene three, Romeo arrives at the Capulet tomb and proceeds to open the vault. Unfortunately, Paris attempts to intervene and Romeo ends up killing him before opening the tomb and kissing Juliet one last time. Romeo then drinks the poison and dies before Juliet wakes up to discover her husband dead.

It is in act 5, scene 1, that Romeo learns of Juliet's death from his servant Balthazar. Romeo's immediate reaction is to make plans for his own suicide. It is his desire to lie with Juliet in her tomb:

Well, Juliet, I will lie with thee tonight.

Romeo knows of an apothecary who makes drugs from herbs. Romeo goes to visit this apothecary and offers him money in return for poison. Although it is illegal to sell poisonous drugs, the apothecary takes Romeo's money because he is in desperate financial need. In act 5, scene 3, Romeo returns to Verona and heads directly to Juliet's tomb. There, he ingests the poison which results in his immediate death.
What Romeo's plan demonstrates is the strength of his love for Juliet. He would rather die than be alive and without her. Tragically, however, Romeo does not realize that Juliet is not dead. She is just sleeping after taking a potion to avoid marrying Paris.