In reading threads here on TAM and talking to some people, it seems that a majority of people going through a divorce (or are already divorced) have been married an average of 20 years. Seems like a lot of couples are making it past the 7 year itch and waiting for the 20 year 'itch' to leave the marriage. In my case, my STBXH started his affair right before our 20th anniversary and now we're divorcing. Could it be MIL? No idea.