Dear Stressed
I want to say ***** and hope that you find the support you need on this site.
It is not difficult to see why you would have such strong feelings of anger and resentment, given what you have been through.  It is good to express them in a safe place like this, too, and know that you are heard.  I suppose one of the problems, though, is that these feelings can end up harming YOU, whilst having little impact on your husband (or his mother, for that matter).  I think your post is saying you ARE really full of these negative feelings, but that you WANT to be different – is that right?  I think one of the ways to start shifting things for yourself is to turn to considering what YOU now want and how you can look after yourself, even in this messy situation.
It is not easy to comment on your husband’s addiction in terms of ‘illness’ – compulsive gambling can be thought of as a disease, but you clearly feel that, for you, it would be very different if your husband had suffered from cancer or something physical.  But I would say that he probably feels very bad about himself and certainly did not intend to become addicted when he first gambled.  You are right not to assume all will be well, but if your husband means what he says about not wanting to gamble again, that is hopeful.  However a 3 week treatment period will not have solved all his problems and he will need ongoing support – does he have Gamblers Anonymous meetings to attend?  use online support? have treatment follow-up?  Are you able to talk calmly about what he *****?  But also share calmly that you are struggling but that you want to make things better.
But back to YOU.  You long for a good family life with some money left over after the bills and debts are paid, of course.  You are working very hard to keep things going.  What can you do to treat yourself from time to time? – give yourself a break?  – think of fun things for a while?  Doing something for yourself doesn’t have to cost a huge amount, but you need to relax, forget about debt and bills occasionally and enjoy something that is for you.  It is not a luxury to look after yourself, it is a necessity!  Your post sounds as if you feel no sense of control – you are doing what you have to do and resenting it.  Caring for your self even in little ways can help you feel that you are taking back some control where you can.
I’m not sure I am saying the right things for you here, but you will get other replies and perhaps share in the group sessions and start to work things through.  You sound as if you have a lot of determination and strength, which will serve you well.  It is good to share with people who have also been/are going through the anguish and turmoil of being involved with a compulsive gambler.  I am the mother of gambler, whose life is still in a bad way – he does not live with me, but it is painful for a mother to see this.
I wish you well as you step forward.
 Keep hope alive.