Janie, I have had experience at this. It will be tough, no matter how you prepare yourself. The best advice is to practice this song until you almost can't stand to sing it. When singing, turn to your inward self, and focus very hard on the interpretation of the song. The idea of a focal point other than a person works very well, but be a bit careful that you don't go clinical.

Singing from the part of you that loved this woman, the sharing of the love, not the grief, that is what will carry you.

Mick