I come into contact with my ex-husband at weddings, funerals and various birthday parties. That's more than I can tolerate, really. We don't argue. I treat him with indifference unless he sets out to give me grief, usually in the form of him neglecting to support our children or grandchildren. He's mean with time, compassion and money. However, we keep it civilised.
He did contact me last year, when our eldest son was having a horrible time with ex-DIL denying access to his son, and his business was going rapidly downhill. As ex is a chartered accountant, I had asked him to assist our son. He was no help at all, attempted to lecture him. We worked things out without him. However, he perceived my request for assistance as a sign that I wanted to be friendly (I invited him and son to my house and fed him whilst we talked). I told him that, when I hear that he is behaving more like a supportive father, he will notice that I am being more friendly. I put the phone down on him then. Last time I saw him, he looked sheepish and made no attempt to speak to me. He hasn't changed.