PAVILION, SELSEY. Joan Fontaine returns to the R.K.O. Radio in one of the best roles of her career in "FROM THIS DAY FORWARD". An up-to-date romantic drama, which depicts life as experienced by many thousands of young people in this country today. She plays a young wife who manages to preserve her marriage through all the trials and pitfalls of modern day life. Mark Stevens, who makes his debut as a leading man in this film, plays opposite the star. "BEWARE OF PITY" which comes on Thursday has Lilli Parker, Albert Lieven, Cedric Hardwicke and Gladys Cooper in the lead.