My ex and I split up two years ago. We were together for nine and I just found out..?

I just found out that he has stopped in to see my biological grandmother 2x, with one visit being just recently. He is back in the same state as she is, as he just recently moved back to that state. I received a b-day card from my bio grandmother, and at the end is where she told me that he stopped in. She gave no details, so I called her and asked why he stopped in. She runs an espresso shop, and for him to even be visiting my family members after him nearly killing me is terrible. He was extremely abusive. Here's part of the problem. My bio grandmother has always had a lustful spirit on her, and it was revealed that she was having an affair with her adult adoptive son. Yes, I know this is all sick. I was raised by adoptive grandparents by the way, thank GOD. So what should I do about this. I talked with my bio grandmother about this and she basically said that she just won't tell me in the future if he comes in to her shop. Also, he had to drive 1.5 hours just to get to her shop, so the visit was intentional. Please, I need some advice on what I should do, if anything.