why did Susan leave Michael?

I actually found this to be the biggest mistake of the movie, at least within the movie's world. Not only would basically anyone familiar with the lead up to becoming deaf understand the physiological nature of the outburst, but with Susan being a scientist, it would've made that understanding far too definitive to assume she would've taken it as personally as she did, let alone so much so that she had to abandon the relationship altogether until another physiological behavioral change made her forgiveness inevitable.

I've thought about it a bit and I just cannot think of anything that makes this a plausible situation. Hopefully someone else can shed some light. Otherwise, I enjoyed the movie.

Rationality goes out the window when you tell a women she's just a "C" word. He could have told her it in a dream and she would have still been pissed.

"It means that I, like God, do not play with dice and do not believe in coincidence."

What he said to her hit a little too close to the bone. She probably knew what the cause of it was, but that didn't matter. The infertile issue is something she's never shared with anyone, and it has screwed up her life. To have it thrown in her face with no warning, and after a most intimate life decision (moving in) was too much for her.

I have a bit of insight into this...

My sister is mentally ill, and she has said some of the most hateful, vile things to me. It hurts every single time. Enough to make me unreasonably angry. Even though I know it's "the sickness" talking, it doesn't make it any easier to hear those things from someone I love.

So that's why she left. Because someone she loved was saying the most horribly cruel things he could think to say to her, and it's impossible to reason with oneself in that position.

Rationalizing that his angry outburst was involuntary doesn't negate her human instinct to feel hurt by the specific things that he started yelling. His anger wasn't simply all-purpose rage, it was directed at her in that moment and he went straight to all of her known insecurities: being infertile, wanting to feel special, commitment issues, and don't forget that he'd confessed to abandoning a serious girlfriend in the past when things became too painful with her. So how could Susan not wonder, "well, there's a good chance he'll drop me too, any minute now." And then shortly thereafter she became unable to comprehend or hear him reaching out with remorse. It's really awful to me, the idea that everyone in the world would have their final sounds be those of horror or violence.

The other huge reason she'd be depressed and isolate was her inability to help. Guilt. Her job should be to save the day in situations like this, yet she was powerless because it sounded like there wasn't even a pathogen to study. It seemed like more of a spiritual phenomenon, in which case scientists would be no more equipped than anyone else. To witness such essential aspects of life being stolen from those you love could be just as, or possibly harder to accept than it happening to yourself. She ran off to her sister and tried to act like he was no one special to protect her heart from even more loss, I think, but in the end she instinctively needed and wanted him anyway.

Blah blah blah....

It was a fault in the plot. No doubt.

All the posters trying to rationalize it is silly.

It was lame. No way a doctor who specializes in this very crap is going to have that reaction.
The OP was right. She would have just walked away until his rage attack was finished.

It's not plot hole or mistake. Most people here are wrong.

She left him because she thought he said the truth.

She suspected Michael from the beginning the he was "smooth *beep* She knew that it was the disease that brought it out and forced Michael to tell her, but it was the truth nonetheless. She felt it proved her right after all.

And indeed, she was partly right. Michael was the smooth *beep* she suspected him to be. He indeed treated women like that, we learned that from the beginning of the movie. The way he kicks out the one-night girl and his friend on the kitchen explains his personality. Michael wouldn't have revealed this side, unless he wanted to stop having sex with her.

But, what she didn't know Michael this time felt a little more. Or needed a little more. It can be interpreted as Michael, the smooth *beep* was in love for the first time. Here goes the irony.

It's not plot hole or mistake. Most people here are wrong.

She left him because she thought he said the truth.

She suspected Michael from the beginning the he was "smooth ar$ehole". She knew that it was the disease that brought it out and forced Michael to tell her, but it was the truth nonetheless. She felt it proved her right after all.

And indeed, she was partly right. Michael was the smooth ar$ehole she suspected him to be. He indeed treated women like that, we learned that from the beginning of the movie. The way he kicks out the one-night girl and his friend on the kitchen explains his personality. Michael wouldn't have revealed this side, unless he wanted to stop having sex with her.

But, what she didn't know Michael this time felt a little more. Or needed a little more. It can be interpreted as Michael, the smooth ar$ehole was in love for the first time. Here goes the irony.