If this is a breakup situation, it's also possible to highlight that the OP would not be effective in the new company - and that maintaining the existing corporate structure would be suboptimal for the other founder.

Now, there is a separate question here of why the other founder wants to use this code in their new venture. Are they interested in the branding etc. from the OP? Is the staffing agency truly orthogonal? There might be "interesting" arrangements to be made for a new corporate structure via affiliate marketing etc.