Why is my ex angry with, and trying to control me?

Divorced 8 months, have son with 50/50 custody. My ex began a relationship with a man 15 years her senior prior to separation, though he lives in another city. I do not interfere in her life though I think separation was a mistake. Our relationship was not abusive. But she is often very angry with me. For example, she dressed me down in public because I didn't invite her to a dinner party with mutual friends. I have ceased contact, except for matters concerning our boy. She tells me off for being too 'lenient' with our son. She drops by occasionally. She told me off for telling our boy 'I miss him' (said it undermined her). She is quite the bully, but oddly, I would take her back, if she made some changes, but she won't take any responsibility for the break-up. Our boy has a strong preference to be with me; he ociates her new man with the break-up. I want us to be civil for our boy's sake but she has these sporadic outbursts. So, why the anger? isn't she happy with her new man?