My mother has always tried to be more my friend than a parent. Sometimes this is sweet, sometimes it's embarrassing, but lately it's become positively nauseating. She's started having an affair (and she's still married to my dad) and can't wait to tell me all the lurid details. I've told her I don't want to hear them but even after I threaten to tell my father—who’s been a wonderful husband to her—she keeps the stories coming. How do I deal with her? And should I really tell my dad?