I think that the meaning is pretty clear she's trying to figure out what went wrong in her relationship with her girlfriend but also what she could have done to make her girlfriend try harder to make it work also and almost blaming herself trying to figure out where she failed knowing that she herself let her heart lead her down that road but also realizing that everyone at some point in their lives has to "walk alone".
I think that the meaning is pretty clear she's trying to figure out what went wrong in her relationship with her girlfriend but also what she could have done to make her girlfriend try harder to make it work also and almost blaming herself trying to figure out where she failed knowing that she herself let her heart lead her down that road but also realizing that everyone at some point in their lives has to "walk alone".