Move on. It doesn’t sound as if there is any damage to your income or reputation. Focus on moving forward not looking behind.
You are right though, most likely, I can just move forward and forget about all this
Rather spend your brainpower on making the product better. Steer the product towards a future where this code leak is irrelevant because the product moved forward so much. Leverage this negative experience to make sure you'll remain the customers' preferred choice even if they can get today's version for free.
Product is so much more than the code. You have assets which you may not yet see as such:
- mistakes made and learned from. These can also come in form of code in the automated test suite.
- machinery around the product: cash flows, relationships between people involved (inside the team, and with customers)
- market insights