This is one of the reasons why I love Suzaku and Euphie's relationship so much... I always thought that Suzaku, after killing his father, believed that he didn't deserve to be happy or be loved anymore... But then he met Euphie, and she shared many of his beliefs (peace, pacifism, an ideal world where everyone could be happy and could be achieved through non-violence), and not only that, but she LOVED him... And so he believed that he could be happy again... But then she was killed, and so he lost a huge part of his soul when she died =(
ITA, especially #5