My childrens father does not want me talking to his fiance.....?

Based on the cirstances you describe, what you did was not only appropriate, but the only moral thing to do. You could probably fix this rather easily for the future by mentioning to the fiance that talking with her upsets your ex, so please simply do not tell him when you talk. Since you're not doing anything wrong when you talk to her, what he does not know truly won't hurt him.