[throwaway010718]

Before quitting, try your best to make changes that will reduce stress and improve the project's manageablity with or without permission. Your work sounds so mission critical you could probably do whatever you want with no chance of getting fired.

Just be able to justify your action and communicate your decisions clearly. You'll start earning respect and that alone will reduce your stress levels. Standing up for yourself is hard to do at any age and "learned helplessness" is a concern if you don't push yourself.