In order to forget him, she needs to give up a part of herself because they used to be so close that he is like a part of her. She has to stand in the rain and let the heavy rain take the sad (and happy) memories with him away.
“I will sink down/ And you’ll be washed away/You’ll be washed away” means that only when she sinks and a part of her disappears can she totally forget him. She’ll give up this part of her soul as a gift of his funeral (of course metaphorically). After this ceremony, hopefully he will be washed away, so that she can finally continue her life without him.
Here's my interpretation of the song: https://en.lineday.co/rachael-yamagata-over-and-over-lyrics-meaning/
In order to forget him, she needs to give up a part of herself because they used to be so close that he is like a part of her. She has to stand in the rain and let the heavy rain take the sad (and happy) memories with him away. “I will sink down/ And you’ll be washed away/You’ll be washed away” means that only when she sinks and a part of her disappears can she totally forget him. She’ll give up this part of her soul as a gift of his funeral (of course metaphorically). After this ceremony, hopefully he will be washed away, so that she can finally continue her life without him. Here's my interpretation of the song: https://en.lineday.co/rachael-yamagata-over-and-over-lyrics-meaning/