We can view how much Othello loves Cassio but he can't be his officer due to reasoning.

Quote #5 & 6

“I know, Iago, Thy honesty and love doth mince this matter, Making it light to Cassio. Cassio, I love thee, But never more be officer of mine” (2.3.262-265).

“O, that's an honest fellow! Do not doubt, Cassio, But I will have my lord and you again As friendly as you were” (3.3.5-7).

Within this quote we view how Desdemona assures that Cassio and her husband will be as friendly such as that of their previous relationship.