You might want to start by looking in Act II scene 1, when Othello comes back after fighting the Turks and successfully defeating them. As he returns, he is overjoyed to be greeted by Desdemona. Note the words that he uses when he sees her:
If it were not to die
'Twere now to be most happy, for I fear
My soul hath her content so absolute
That not another comfort like to this
Succeeds in unknown fate.
Note the expressions of love in his words. The sight of Desdemona after battle makes his soul so contented that nothing else could increase that sense of contentment. Even if he were to die, he could die in a state of perfect happiness because of his love for Desdemona and the joy that seeing her brings to him. It is clear that these words from Othello describe a man completely in love with his wife, and entirely devoted to her. It is worth tracing the way that his affections change as Iago works his terrible work.