My DH has had a gambling addiction since he was a teenager. Before we met, he would also gamble in the 1000s and live in the euphoria of the ups and downs / famine and feast that it brings. He has told me that it is precisely this instability that feeds the thrill. And in his case, he has said the downs push him to succeed in his career. He is one to focus on earning more, instead of spending less. He is incredibly smart and knows exactly the consequences - both financially and emotionally - it imposes on us.
Once I found out the true extent of his addiction right before we married, we tried several that progressively got it under control (from 1000s to 100s to 10s to nothing for 3 months now). This has only been possible because of his real willingness to change. Yet he acknowledges that he will always will be a gambler, risk-taking is part of his personality and though some steps can be taken to minimise it, it is his "dark passenger" for life.
Here are a few things that he/we have done:
1- No more credit cards. The only credit cards we have are in my name; he has one which I keep in his name for emergencies and I am the account holder so get to see everything that is spent on it.
2- Joint account. His salary goes straight into it. I hold both debit cards, he does not carry his anymore. I subscribe to the bank's text alert messages, and even before DH relinquished the debit card I could always be on top of any spend. After trying him sticking to an agreed gambling budget and failing miserably for years, we have recently agreed take out cash and give him on a as needed basis for petrol, lunch, etc.
3- Pre-paid debit card. Before going for the cash-only solution, we tried a period where he had a pre-paid debit card. I would credit a set amount per week which was his gambling/entertainment budget, which we both agreed to.
4. Ban from betting shops. Also before the cash-only solution, he banned himself from the bookies around the area we live and near his work. This step in particular was a really big one, and only happened after several episodes that caused a lot of heartache for both of us. It took him a lot of courage to go through it, especially as he felt it was really humiliating to have to go through it. It was a final acknowledgment that he lacked any control over his behaviour.
The plus side of all of the above: we finally have financial stability, he has restored a sense of pride and self-respect and we have rebuilt our mutual trust. The downside: all the financial decisions and management are my responsibility which can be a big burden. It also removes a lot of spontaneity from his part- eg, he can't buy me a present by surprise without me knowing. Also, there is a big emotional impact - a feeling of dependance (him from me), a feeling of resentment from me (to have to make all big decisions and add one more thing on all things I do for our family...). I think in the short-term it also made him feel emasculated and this had a negative effect on our sex life. But after several years, two DC later I can honestly say we are stronger than ever, our mutual admiration has grown ten-fold, our love and sex life are great (well, as great as it can be with two under 5s) and we have definitely evolved as people and as a couple.
Sorry for the long post, I hope any of this is useful! 