How is the theme of LOVE responsible for Romeo and Juliet's death?
The love of Romeo and Juliet is a violent love; as such, it affects death.
In Act II, Romeo comes to Friar Laurence and pleas with the priest to perform the marriage ceremony for Juliet and him; afterwards, the friar tells Romeo he hopes that Heaven will smile upon this marriage and sorrow not come to such a dangerous match. But Romeo recklessly replies,
...love-devouring death do what he dare.
It is enough I may but call her name. (2.6.7-8)
To this remark, Friar Laurence cautions,
These violent delights have violent endsAnd in their triumph die, like fire and powder,Which, as they kiss, consume. (2.6.9-11)