Complex sentence: Barney heads off to the shooting range and apologizes to Robin: for preparing a wonderful date for Anita when he never tried it once with Robin; he decides to let Robin and Don go the "super-date" and promises he will not sleep with Anita.
Split into simpler sentences: Barney heads off to the shooting range and apologizes to Robin for preparing a wonderful date for Anita when he never tried it once with Robin. He decides to let Robin and Don go on his super-date, promising as well to Robin that he would not sleep with Anita.