This is about a relationship that is about to be terminated. Maybe the woman has cheated on the singer - something like that anyway - and now he's saying (in his mind at least) it's over. She's "sly, sly, like a demon's eye" as far as he's concerned. He doesn't care what she says now, his mind is made up, it's the end of her time with him (even if she doesn't know it yet). He's been rejected by her, and now he's rejecting her also. It's all over rover...
This is about a relationship that is about to be terminated. Maybe the woman has cheated on the singer - something like that anyway - and now he's saying (in his mind at least) it's over. She's "sly, sly, like a demon's eye" as far as he's concerned. He doesn't care what she says now, his mind is made up, it's the end of her time with him (even if she doesn't know it yet). He's been rejected by her, and now he's rejecting her also. It's all over rover...