What does it mean to
PLAY SOMETHING BY EAR?
If you play a piece of music by ear, it means that you are playing it from memory, without the music in front of you.
If you play a situation by ear, it means that you will not plan ahead but will make decisions as they arise.
A: Do you want to meet to study together again after class tomorrow?
B: Let’s just play tomorrow by ear and see how it goes. I have a big project due this week and I’m not sure how much I will get done this evening. I might have to work on it tomorrow after class.