What seems to be Othello's primary motivation?
It depends on what part of the play we find Othello in. In the beginning of the play, Othello is motivated to be the best, most competent general he can be. He is capable, brave, and reliable (along with skilled). He is also motivated by his love for Desdemona. He wants her to be proud of him.
Later in the play, once Iago has convinced him that Desdemona is having an affair with Cassio, Othello is motivated by jealousy. He lets jealousy overtake his sense of logic and reason, which is his tragic flaw. He becomes more enraged with jealousy as the play continues, until he murders Desdemona.
I think Othello's own sense of pride and ego are his primary motivations.
Since he is "the Moor of Venice", many already look at him as a curiousity. This makes his deeds as general greater and offer a boost to his ego and pride. The ability to win the love of Desdemona furthers this positive sense of self.
Though he takes on the role of a wounded lover when he suspects Desdemona of infidelity, his pride and ego are also wounded.
This further fuels his gowing rage which ends in the harm of Desdemona.