You two should definitely break up. She had the courage to take a chance on you because she thought you were worth it. Clearly you aren't. Just have the goddamn decency to be nice about it.
As a side note to the people who say she should have told him first: heterosexual transgender people (especially trans women) do not have an easy time finding non-transgender partners who are totally okay with their medical history. Hence, I can understand why they would want to wait until the relationship starts getting serious: they want their potential partner to have the chance to evaluate them as a -person- with interests, hobbies, pet peeves, etc. instead of writing them off completely at the very beginning.