Complex sentence: The reason why is because that after communism's fall, his wife left him for a German tennis player and his son turned to sports and selling Halloween costumes for dogs, so he vowed that one day he will get his revenge.
Split into simpler sentences: The reason why is because that after communism's fall, his wife left him for a German tennis player and his son turned to sports and selling Halloween costumes for dogs. So he vowed that one day he will get his revenge.