Dear Barbara:
You are not a bad person for feeling the anger that you feel, feeling excluded and so forth. We are not guilty for how we feel, no matter what it is that we feel.
On the other hand we are sometimes guilty of our behavior, when your behavior is not fair to others. In this particular case, his children should come first in his life. He is their father, he owes them time and attention. Therefore anything you do to keep him away from being a present and attentive father to his children, is bad behavior on your part.
I suggest that if it is too difficult for you to be in this particular relationship that you pause it or end it altogether. And make a decision: in the future, choose a man who does not have minor children.
anita