Elvis Costello - Alison Lyrics Meaning

Still in love with Alison.... probably a really hot girl who never gave him a chance. Other guys were lifting up her party dress. She is a flirt. Now he is disgusted to learn that Alison has become a porno actress. He wishes someone would "put out the big light", i.e., the bright movie projector light that illuminates 20-30 foot images of her on the screen. He knows that "this world [porno] is killing you". His "aim is true", that is, his motive and intentions are pure, to stop her from this sinful life; also double meaning - - his accuracy and "aim" will be on point as he will shoot out the projector bulb if need be. "sometimes I wish that I could stop you from talking when I hear the silly things that you say" - - this song is from late 70's - - porno films were cheesy and poorly produced with awful dialogue. He sings "I can't stand to see you this way..."