Need avice

Need advice. I've been in a relationship with a woman for 2yrs but she didnt know my real gender that im a lesbian. She knows im a man. I dont know if she ever have a hint or whatsoever, I tried many times to break up with her to avoid finding out the truth but she didn't want to. I badly want to tell her the truth from the beginning but im scared of what she gonna do because i know how crazy she is when we're fighting. Im scared i dont know how to tell her i want it to be over. im so guilty.