Carmy knows Sydney didn't sign the partner agreement. (usually with docusign, all parties involved are informed when a document is signed from each participant) He hasn't asked why yet and is waiting for Sydney to tell him why.
Look at this look. He is waiting for the bomb. He knows something is coming. I am a firm believer that carmy is intuitive and he ALWAYS KNOWS what is coming. He watches Sydney often. He's observed her, quietly. Learning her. He knows something is up and he absolutely has an idea of what it is.
Carmy is in his own mental spiral, sure but he is aware of what he's doing; how he's behaving. Is he aware that Sydney has decided to leave? maybe. Is his anxiety telling him she will leave? most definitely.
I've watched this clip a bunch a times I feel as though he comes to so many realiziations in this moment. As soon as Sydney says they need to talk...you can see him mentally prepare for the bomb. I honestly can't wait for next season because he has to fight for her partnership in all avenues. If he truly wants it, he'll fight.