OK no, that's not cause to go shit-talking her. Getting a crush on a teacher is stupid but as long as she didn't act on it I don't see why you consider it committing an offense against you, and if she did it would be the teacher's responsibility as an adult to reject her and shut that shit down anyway. Not your place to punish her for dumb feelings by telling other people about it, which will get her mocked mercilessly and if the wrong person hears it and jumps to conclusions it could also get the teacher in trouble despite them not having done anything at all. That would be very irresponsible behavior on your part, and I'd call it immoral too. Keep this whole situation between the two of you. And finally, based on this and everything else I've read in this thread I'm also gonna recommend you two go your separate ways and that you wait a while before you start dating again.
EDIT: I meant start dating in a general sense, not start dating her again. I don't think there's a positive future in this, and I recommend you just move on