If you look at the immediate causes of the deaths of the people in the play who die, Romeo caused the death of Tybalt (he stuck a sword through him), Paris (he skewered him too) and himself (he drank poison). With the other deaths, you can argue that the other people would never have died if it hadn't been for Romeo, but you can create similar arguments for just about everyone in the play. The fact is that Tybalt, not Romeo, sticks a sword in Mercutio, Juliet, not Romeo, sticks a knife in herself, and Romeo's mother must be made of feeble stuff if she dies because Romeo has to move to a different town.
poison
Romeo and Juliet kill them self's. Romeo kills himself with poison and Juliet kills her self with Romeos Dagger.
In Juliet's tombafter drinking poison to kill himself.
He drinks poison, in Juliet tomb to "die with her", thinking Juliet was really dead. And Juliet stabbs herself when she see Romeo dead.
Romeo buys the poison to kill himself because he does not want to live without Juliet once he finds out that she is "dead".
He decides to kill himself at her tomb with poison.
She tries to kill herself with the remains of the poison he killed himself with.
The potion that Romeo buys is poison and he buys it because he wants to kill himself after thinking Juliet is dead.
When Romeo learned Juliet was 'dead' he bought some poison and went to Verona to kill himself because he felt he couldn't live without her.
They try to solve the problem by?
Romeo... Takes deadly poison, that kills him in seconds 'thy drugs are quick' (Act 5, Scene 3, Line 120) Juliet... Stabs herself
Romeo kills himself during Act V Scene III.