There are (at least) two verbs spelled「いる」. The verb indicating presence is a -る verb (hence 「いない」), while a verb meaning "to need" is a -う verb.
While, yes, either one would make a grammatically correct and comprehensible sentence, which one is used obviously changes the meaning of it. The meaning was whether she has a boyfriend or not, hence 「いない」and not「いらない」.
These are actually written with different kanji as well (when they are used)「居る」 for presence and 要る for "to need".
今彼氏がいない = Doesn't have a
今彼氏がいない = Doesn't have a boyfriend now.
今かれしがいらない = Doesn't need a boyfriend now.
There are (at least) two verbs spelled「いる」. The verb indicating presence is a -る verb (hence 「いない」), while a verb meaning "to need" is a -う verb.
While, yes, either one would make a grammatically correct and comprehensible sentence, which one is used obviously changes the meaning of it. The meaning was whether she has a boyfriend or not, hence 「いない」and not「いらない」.
These are actually written with different kanji as well (when they are used)「居る」 for presence and 要る for "to need".