Why did Gladstone and Disraeli hate each other?
Gladstone was from a different class and religious background to Disraeli, and resented the notion a middle-class Jew could come from nowhere.
While Gladstone had an old-school personality which emphasized loyalty, Disraeli was opportunist and pragmatic, even shameless.
At that time, people in politics (in opposing parties) didn't become friends like they do today.
Disraeli gave the vote to more people, which was controversial.