If you are a teacher in a school system, you could ask for a transfer to remove yourself physically from his presence. That probably can't happen until next school year, but it would certainly be something you could look into (I would).

In the meantime, set some boundaries. Make your communication with him only about school-related business. Otherwise, you have the power to stay away from him. Continuing to communicate with him in a personal manner is unnecessary and leaves you in situations that apparantly are confusing. If he's still leading you on while with this new girlfriend, sounds like you have dodged a bullet with him. This seems to be a pattern of behavior for him that would have doomed your marriage anyway. Try to keep that perspective.