My co-founder just got a job and didn’t tell a couple of people who are working effectively for free right now. I didn’t even knowIs that right or is that wrong?

Well if your co-founder cannot afford his rent and will have to drop out or go homeless, then this doesn't seem to be such a bad decision.

We'd need more context on why you think he did it.

They should have told you before taking the job, and made sure it didn't impact your startup. Are they leaving the startup, or doing both? If both then be sure to find out which one they are prioritizing in terms of time. If there is little or no income in your startup yet, then I can understand them needing to supplement their money, but co-founders should be transparent and work together to look after each other and make sure there are no sudden surprises that could cause disruption to schedules.

As long as they pull their weight. If you're not paying their bills, you can't be picky.