"Family Guy" creator SETH MACFARLANE will guest-star on the season finale of "The Simpsons" on Sunday, May 19th.  He's voicing a "charming man" who meets Marge after she inadvertently hits up an Ashley Madison-type website. Like Marge, Seth's character is married.  Comedienne LISA LAMPANELLI is voicing his wife.  (In October, Dan Castellaneta . . . the voice of Homer Simpson . . . made a guest appearance on "Family Guy".)