Crikey keep out of it, your sons needs to be getting involved in this like a hole in the head and whoever gave him the ultimatum needs to grow up. No-one know IF this happened, and if it did no-one knows WHY this happened, she might have owned up by now for all you know or they might have an open relationship and if so then the friend won't thank anyone discussing it anywhere. Equally it might have been a one off terrible error of judgement. People and their relationships are best left alone.