My interpretation of My Love, is that Sia is singing about a love more powerful than any other. The line "leave yourself behind" is supposed to represent the lover putting her first. She often mentions in the song that the love has made her stronger, and that the love between the two of them has taught her honour. In the line "in peace you'll go" it gives me the assumption that the lover has left her, whether it be in a break up, or in a distance, or even in the lover's death. I can also back this (slightly morbid) idea up with the line "beat inside me" where she is requesting their love forever more; it is as though something has happened to damage this perfect love that she felt.
I hope this was helpful!