A lot of people saying you own 40% of this startup so you need to fight for it are giving you bad advice. Based on what you said, you don't own anything yet because you haven't vested any shares.
If you are a Corporation, and your corporation is setup in a standard way with your partner as the CEO, he can fire you. They only thing you can do is go to your board of directors and plead your case. The board has the ability to fire the CEO, so they can force him to retain you.
If you are an LLC, then you don't really have a cap table and there is a good chance there is no vesting. You have something else. You need to read your operating agreement. It will define who has the real ownership and how the buy out process works.
If you are a Corporation, and your corporation is setup in a standard way with your partner as the CEO, he can fire you. They only thing you can do is go to your board of directors and plead your case. The board has the ability to fire the CEO, so they can force him to retain you.
If you are an LLC, then you don't really have a cap table and there is a good chance there is no vesting. You have something else. You need to read your operating agreement. It will define who has the real ownership and how the buy out process works.