It’s often used casually when someone was expected to show up but didn’t—or seemed like they wouldn’t. Other ways to say it: I thought you weren’t coming. I thought you ditched me. (very informal) I thought you flaked on me. (slang) I thought you changed your mind. I thought you backed out.

I thought you -left me I thought - you changed your mind I thought- you weren’t going to do what we agreed To ‘bail out’ is to leave or to get out of a situation