[monoideism]

> As I understand it, we're having a very difficult time finding people.

Another possibility is that they don't have enough money to hire another developer, but don't want to admit it to you. Start-up life can be harsh.

Don't burn yourself out. I can tell you from experience that it gets harder and harder to come back from burnout each time it happens. If your workload is ridiculous, it may be talk to your boss about adjusting timelines/expectations to something more realistic, or even time to start looking for another job.