Dear Ell
You are an amazing woman.   I too would struggle not be***ve the evidence of my own eyes but I agree your husband cannot prove that he did not take the money.  
If he told you that he had taken the money what would your reaction be?   I suspect that whatever did happen your husband will be shaking in his shoes at the wrath that would come down on him if he said he had ****.   It is, I be***ve, one of the greatest conundrums the non-CG faces – the ***** is worse than the loss of money but the CG cannot comprehend that.   They will *** through fear and maybe it is a justified fear – we are, as you so rightly say, only human and as humans whose trust is shaken, we feel great anger.
I agree that you will always know what is in the box and I think it is unwise to forget.   It is possible to close the box though, with a struggle and I admire your wisdom in doing so the way you are.
Find the model Ell – it does exist.   I t does mean, I think, that some***** we have to be silent but if necessary there are ***** we have to roar.   Unfortunately roaring against the addiction to gamble does not make it listen but the non-CG ***** the outlet – this forum is always here for that.  The middle road is of course ‘discussion’, keeping the lines of communication open and the CG aware that you have not forgotten, without constantly reminding them in an obvious way.    Certainly I be***ve that cash should never be left ***** around or easily accessible – rather than seeing it as lack of trust, I see it as fighting the addiction on the loved one’s behalf.
I have guests for the weekend ‘again’ but I will be back next week to read your thread.  I suspect that he did take the money because in a lapse of complacency he be***ved he was not a CG – he has been saying he found it easy to not gamble – it is not.   Your husband’s counsellor, I think, should be in possession of the knowledge of this loss of money as he too seems to think that all is well – complacency is the devil on the shoulder of the CG and many counsellors do not appreciate the deviousness of the addiction.
I hope this makes sense.  I came on to see if you had written but I have got a house to clean and tidy before my guests come.  I have been watching the tennis at Wimbledon for nearly 2 weeks and the dust is thick!
Look after Ell and baby Ell and also Mr Ell.   In my opinion, his addiction is stronger than he realised and you are ahead of him in understanding.