They are married. It would be hard to have a story about marital jealousy if they weren't.
othello
Othello
Desdemonas father and one of the senators of venice.
desdemonas pity of othellos life struggles
The significance of Desdemona's relationship with Othello is that she marries him dispite knowing her father would not approve. Othello was a black man and was looked down upon because of his race and color. Shakespeare was tackling the race issue way ahead of most people.
They had a good relationship - Othello trusted Cassio and Cassio respected Othello
Iago doesn't like other people to be happy because he is so unhappy himself, notwithstanding the fake "honest Iago" persona he has developed. Since Desdemona is happy in her marriage to Othello, Iago wants to destroy her in the process of destroying Othello.
Cassio and Othello were very close friends before the play.
Desdemona's father, Brabantio, is upset about her marriage to Othello because he feels betrayed and believes that Othello has used witchcraft or manipulation to win Desdemona's affection. As a Venetian nobleman, he harbors racial prejudices against Othello, a Moor, and is distressed by the idea of his daughter marrying someone outside their social and racial circle. Brabantio's anger is compounded by the notion that Desdemona has defied paternal authority and societal expectations.
Desdemona exhibits qualities such as kindness, loyalty, and innocence. She is portrayed as a devoted and loving wife to Othello, displaying patience and understanding in her interactions with him. Desdemona is also known for her boldness in defying societal expectations by marrying Othello against her father's wishes.
Brabantio(a senator)
Casio thinks of Iago as a very dear friend to Othello, but to Iago Casio was a toy to make Othello jealous. what they both have in common is that they both serve under Othello and are dear friends in battle to him.