It is a good representation of the concept of Rin's bisexuality and feelings toward Saber. It handles the subject matter accordingly, and is a bit interesting regarding where it will most likely go from here. There were some good literary techniques at play as well with the beginning.
As with most fanfictions, the grammar and tone could use some work. As well, the change in the center of the story from the perspective of Rin to Saber's dream could have used some work as it was unclear of what was occurring at the beggining, combined with there being no descriptions toward Saber in this period and only being referred to as "She" make it a bit confusing. I am aware this was meant to be done for mystery sake, leaving it in the air until the reveal, however it can still be achieved with some descriptions and nouns. This could be remedied by replacing some of the "She"s with "A Woman." Or, "The Blonde", etc.
I look forward to more.