Well I believe the reason he committed suicide was because incest is a taboo in many societies. We constantly hear things like "incest is a sin", "incest is immoral", "incest is disgusting". We Are conditioned to believe that incest is one of the worst possible things you can do in life so what do you think that does to a person's mind? Shinobu must of constantly had these thoughts in his mind he must of thought he was a disgusting sinner for having a relationship with his brother and son and he couldn't take it. To top it off he betrayed his wife. And his lover was a man another thing society looks down upon. So yeah Shinobu must of thought he was a terrible human being when all he was doing was the one thing us humans can't help "falling in love". I think deep down Shinobu knew that he would never be able to have a normal happy relationship because societal views would never allow it. So sad but amazing story.
Could someone tell me why he would just go out and kill himself after all that and him being in love? my head just keeps spinning not being able to understand why.