How does Romeo react to Balthasar's news in Act V Scene 1?

Balthasar reveals to Romeo that Juliet is dead in Act V, Scene 1. He tells Romeo,

Her body sleeps in Capels’ monument,And her immortal part with angels lives.I saw her laid low in her kindred’s vaultAnd presently took post to tell it you.

In a case of dramatic irony, Balthasar knows nothing of the Friar's plan for Juliet to fake her death and in the next scene the audience finds out that...

Balthasar reveals to Romeo that Juliet is dead in Act V, Scene 1. He tells Romeo,

Her body sleeps in Capels’ monument,
And her immortal part with angels lives.
I saw her laid low in her kindred’s vault
And presently took post to tell it you.

In a case of dramatic irony, Balthasar knows nothing of the Friar's plan for Juliet to fake her death and in the next scene the audience finds out that Romeo doesn't get the message from the Friar announcing the plan. Thus, Romeo reacts as he does throughout the play. He leaps to action without considering the implications of those actions. He is predictably impetuous. Upon hearing the news he launches into a plan to commit suicide in the Capulet tomb next to Juliet. He says, "Well, Juliet, I will lie with thee tonight." He orders Balthasar to "hire post-horses" so they can immediately go to the tomb and he finds a poor apothecary (pharmacist) to buy poison from. He actually bribes the apothecary because it was against the law in Mantua to sell the substance. He is so bent on his plan that he even kills Count Paris outside the tomb when he arrives. Had he been just little more introspective, he may have not been so hasty. The Friar actually arrives in the tomb not long after Romeo has taken the poison.