Complex sentence: However, he suffered from severe depression and alcoholism and on May 11 1994, Puller won a Pulitzer Prize for his 1991 autobiography "Fortunate Son" nut it wasn't enough, he died of a self-inflicted gunshot wound to the head.
Split into simpler sentences: However, he suffered from severe depression and alcoholism and even though Puller won a Pulitzer Prize for his 1991 autobiography "Fortunate Son". The recognition the book won him did not prevent him from taking his own life on May 11 1994 from a self-inflicted gunshot wound to the head.