1.
because of; due to (negative cause)
Indicates the cause or reason for an undesirable outcome. Attaches to nouns (with の), na-adjectives (with な), i-adjectives, and verbs in plain form.
Derived from 所為 (cause, fault), せいで is used exclusively when the result is negative or undesirable. For positive outcomes, おかげで is used instead.
Usage
せいで follows nouns with の, na-adjectives with な, and plain-form verbs or i-adjectives directly. It can also appear as せいか (softer, less certain) or in the pattern のせいにする (to blame something on).