Complex sentence: Sam and Mark then embark on a casual relationship which includes dates to a cooking lesson and skiing after Sam and sister Billie are attacked her and Mark begin dating properly and Mark's family invite Sam round to eat with them.
Split into simpler sentences: Sam and Mark then embark on a casual relationship which includes dates to a cooking lesson and skiing. After Sam and sister Billie are attacked, her and Mark begin dating properly and Mark's family invite Sam round to eat with them.