You have been inadvertently caught up in the cycle of the addiction to gamble and not known where to turn – I’m glad you have found this site where there is no judgement – just understanding.
You have been up one moment and down the next – the roller coaster whipping you along and gradually taking away your control – it is time to put the brakes on so that you can get off.
I hope to read in your next post that he did attend GA and how he has reacted.   It is common for a CG to come home and say they are not as bad as the others – whatever he says, listen but don’t judge – what actually happens he may not tell you the truth.   I did once hear that whatever their reaction they never forget the words at the first meeting.  
I hope that this site can be your rock.   It is a lonely life with the addiction to gamble in it but I will walk with you for as long as you want me to.
Unfortunately I am going away for a few days I am going to bring my thread ‘The F&F cycle’ up for your – I hope it helps to see that you are understood.  
With regard to telling your children we have focussed on this in our friends and family topic forum which is the forum below this.  Maybe there is something there that could help.   My suggestion is that you should gather as much knowledge as you can about the addiction to gamble before you tell others because it is easier to impart the knowledge dispassionately, without leaving an opening for opinions – just questions.
You have done well taking his credit cards and he has done well giving them to you.   These are starter point for a recovery.
Your confidence and self-esteem will have been flattened by your husband’s addiction and although it doesn’t see too great an answer, looking after yourself is the best thing you can do for both of you.   It works because your mind will have been full of your husband’s addiction too and it has been pulling the string of your life.   Taking back control is important –‘you’ are important.  You cannot make your husband stop gambling but you can make a difference.
You have done nothing wrong – without knowledge you never stood a chance and the addiction knew it.   Between us we will reverse that misunderstanding and you will realise that you are stronger than your husband who is controlled – you are not, you are free.  
I might get a change to speak to you tomorrow but if not I will write again soon.  In the meantime, know you are among those who understand.
Well done writing your first post.