Whyd his father kill himself?

It's never specifically stated, but we are told that his loyalty had come into question after being considered for Secretary of the Navy.

This is what was in the suicide note, according to the first page quotes info:

Edward Wilson: [reading] They are right what they say about me. I was weak. A coward. I compromised myself. My honor. My family. My country. I am ashamed of myself. To my wife, I am sorry I've done this to you. To my son, I hope you will grow to be a courageous man. A good husband. A good father. I hope whatever you decide to do, you lead a good, full life. I hope whatever your dreams may be come true. Your loving husband and father.

Semper Contendere Propter Amoram et Formam

Edward Sr. had a brief but passionate homosexual liaison with the late Dr. Fredericks during World War I, which was the personal shame and familial dishonor he was alluding to in his suicide note. Dr. Fredericks never got over Edward Sr., which led to his attempted seduction of Edward Jr. years later. Edward Sr. committed suicide because Dr. Fredericks and the British used the affair to blackmail him into spying for the UK in preparation of their planned invasion of Maine and reconquest of the American colonies.

Hope that cleared things up.

With the moral code Dad explains to little Edward, it could have been anything.

Remember even in modern times, Adm. Boorda (supposedly) killed himself for wearing un-earned ribbons and medals.