In my opinion one of the most important statements made in "Much Ado About Nothing" is that of Claudio's concerning friendship, he says "Friendship is constant in all other things / Save in the office and affairs of love". I say this because in more than one occasion friendships have been broken and trouble ensue just because of love.
The first instance of this is when Don John tells Claudio that the Prince woos Hero for himself. Claudio being gullible and extremely jealous, immediately looses all the trust he has in Don Pedro just because of Don John saying that he heard the Prince "swear his affection".
The betrayal of a friend occurs again when Beatrice asks Benedick to "Kill Claudio". Even though he refuses after this and says "Not for the wide world", he eventually changes his mind after Beatrice says, "You kill me to deny it". He goes to Claudio and threatens to "protest [his] cowardice" if he refuses to fight and if it had not been proven that Hero was innocent, Benedick could have possibly killed his friend.
Throughout the play almost all the characters have had strain on their friendship with another person. For example the friendship between Claudio and Don Pedro with Leonato suffered after Hero was accused of infidelity at the wedding. As well as the relationship between Hero and her father until Beatrice proved that she was innocent for she was her bedfellow. Even though after all of this everyone is forgiven, except Borachio and Don John, and they become reunited.