Complex sentence: Shortly afterwards, Hiro discovers that his health is deteriorating and makes the painful decision to break up with Mika to keep his terminal illness from causing her pain, but continues to follow her whereabouts through his highschool friend, Nozumu.
Split into simpler sentences: Shortly afterwards, Hiro discovers that his health is deteriorating and makes the painful decision to break up with Mika to keep his terminal illness from causing her pain. As Mika goes on with her life Hiro continues to follow her whereabouts through his highschool friend, Nozumu.