The underlined part of the sentence is a restrictive phrase.
nonrestrictive phrase.
restrictive clause.
nonrestrictive clause.

Cláusulas restrictivas dan información esencial en una oración. La oración no tiene sentido sin la cláusula. ... Una cláusula restrictiva empieza con un pronombre relativo.

Explanation:

he is. some of his decisions were very irresponsible and did lead to the death of both romeo and juliet, such as him marrying them too quick or him not clarifying romeo's plan with him.

basically he did not think things through well enough or at all.

hope this