Here is what you should do starting right now.
1. Document everything that you still can. Emails, conversations, records. Get everything and put it into a folder. You will need this in case something comes up later.
2. Quit tomorrow.
3. Go pursue your startup idea. If you need more savings and want to build some up, do some freelance projects which I'm sure others on here would be happy to point you towards. You already said additional money is not a requirement so there should be nothing stopping you from wasting your time.
Again, you owe them nothing.