I have found out that one of our neighbours appears to be having an affair. He is married with a child. We don't really know one another although I know his and his wife's names. I don't know the woman I saw him with.
I don't know whether to post an anonymous note to his wife or not.
I also don't know if my own experience is affecting my judgement. Years ago, one of my neighbours tried telling me my own husband was having an affair. She didn't do it directly and I didn't cotton on so it was only later when I found out about his affair that I realised what she had been trying to tell me. I felt grateful she had tried to intervene.