Identify the main source of conflict, as well as two other instances of conflict in the story

The main conflict in the story has to do with marriage itself, and the fact that the play's primary male characters are suspicious of marriage and afraid the marital state will leave them less than men (controlled by their wives).

A secondary conflict would be reflected in the way Hero is set up by Don John, and a third might be reflected in the fact that each of the characters does in fact wish to be married.