It sounds like to me the concept of ratification applies here and also laches and equitable estoppel.
1. Ratification is the act by a principal [him], after the agent [you] has acted, confirming that what the agent may have done without authority, is binding on the principal.
2. Laches is the unreasonable delay in making an assertion or claim, such as asserting a right, claiming a privilege, or making an application for redress, which may result in refusal.
3. Equitable estoppel is concept where that serves as a bar to a party from asserting a legal claim or defense that is contrary or inconsistent with his or her prior action of conduct.
It further appears to me that the two of you had a partnership even though there was no written contract governing the partnership and in which case the courts may apply a 50-50 approach to loses and profits. Finally, you may be able to argue that the money he took that you may have had a right to he owes you back under the concept of civil conversion.
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