this is a good question because this is easily a situation that could happen.
if i felt for them, id end it due to the lack of honesty. thats something they should have let you in on early, like the 2nd date. that way you have a chance to decide if you're cool with it or not before you develop feelings for them.
id also end it because even though they got the parts changed, it doesn't change the fact that they were a man before. the genetic make-up is still the same, plus you could never have children.