Desdemona and Othello get married and look forward to a happy life together.
War interrupts their romance, but they assume they'll have time together soon.
Welcome to Cyprus, Island of Love
Everything is wonderful with Desdemona and Othello. The newlyweds have each other, they're surrounded by trusted friends (or so they think), there's no war…
Evil Iago convinces Othello that Desdemona is cheating on him. At first, Othello can't believe it, but Iago gradually warps his mind.
Needless to say, it is rather frustrating for a newly married man to be told his wife is already screwing around. This is definitely your teeth-gritting stage.
Othello begins to go almost crazy with jealousy. His love for Desdemona is changed to disgust. He mistreats her, even hitting her in public, and calls her a whore. Desdemona can't understand what's happening to the man she loves.
Teeth-gritting proceeds duly to jaw-dropping, as Iago's machinations increase in complexity and general evilness. Othello's suspicions stop being suspicions and become, in his mind, undeniable truths. The psychological heart of this stage is when Othello commits to killing Desdemona. The physical peak is when he hits her, in public.
Othello kills Desdemona and plans on Iago killing Cassio; Iago convinces Roderigo to kill Cassio but ends up wounding Cassio himself and killing Roderigo; Othello finds out the truth and kills himself, but not before trying to kill Iago, who also kills Emilia.
Keep in mind that this is the destruction not only of everyone's life, but also of the dream that we started with way back in the early part of the story.