withdrawal from a partnership llc, do i need a separation agreement?

From a legal standpoint, there is a difference between a partnership and an LLC. The type of document you would need depends on which of those two types of businesses you have. But in either case, there should have been an agreement between your partners (or LLC members) that addresses this situation. If you have such an agreement in place, review it to understand what must be done in your situation. If you do not have such an agreement, I suggest you see a lawyer in your area to prepare an agreement for you. The reason this is not a do-it-yourself type of agreement is, depending on the language included in it, the agreement could still hold you liable for things that arise in the future. There are a lot of issues to be addressed in the sale or transfer of a business, such as non-competition terms, division of liability, and more. Best wishes.