Legal Question in Family Law in California

There is no way to predict the outcome of a case with any certainty at the outset. When it's based on one paragraph of information from one side it's beyond impossible. If the charges were made entirely for mutual benefit and/or without any agreement on how the balances would be repaid, he has a tough time making a case and I can't see any good way for him to get more than 1/2 if anything. If they were joint accounts, though, you're both liable for the full amount in which case he might have a good case for equitable indemnity for at least 1/2. That's about all I can tell you.