Lovely, sad song. She's acknowledging their relationship is over, and her heart's breaking because she was sure it would last. So she's asking for just one more night, to maintain the fantasy and the happy memories of what once was. She promises him that if he'll grant her that wish, she won't try to make him stay with her, as long as he allows her to imagine he still loves her for one more night.
Lovely, sad song. She's acknowledging their relationship is over, and her heart's breaking because she was sure it would last. So she's asking for just one more night, to maintain the fantasy and the happy memories of what once was. She promises him that if he'll grant her that wish, she won't try to make him stay with her, as long as he allows her to imagine he still loves her for one more night.