This sounds like a typical abusive relationship. You might have more of an understanding about your son’s experience if you read and learned more about why people stay in abusive relationships — the cycle of violence, the hope and codependency they often have, what happens to their sense of personal power and self esteem.

Of course your anger and protectiveness of your son and grandchildren is totally understandable (it is so deeply painful to witness these relationships when it’s someone we love), but you will have a better chance of reaching your son, and perhaps even helping him, if you work to really get how he feels. Then you can speak to him with empathy and be available if/when he becomes brave enough to reach out to you without feeling ashamed.