My Brother in-Law, My Lover

Ashley woke up one day realizing that she loved her brother-in-law. He is her sister's husband, but not just any sister; she is her own twin. She feels guilty and hurt every time the couple is sweet with each other, but she can do nothing because she has no right. She knows she doesn't own her brother-in-law, so she is content with the stolen moments they share.
How far will her betrayal go? What will she do if she discovers everything she believes isn't true?