Many people use gambling as an escape to relieve stress from certain problems, hoping it will make them feel happier and more relieved.
And returning to the initial discussion about why someone might return to gambling after previously deciding to quit, I suspect that the person may be experiencing difficulties or problems that are truly burdensome, causing stress and depression. A situation that could remind them of past behaviors that led them to gambling as an escape from stress. I also suspect that the same reasons may have led them to return to gambling. However, instead of making them feel happy, gambling actually becomes an addiction, which further exacerbates their stress and depression.
Besides the issues of depression is another case scenario of relationship. What kind of relationship did he maintain during the time he quit gambling? If he could answer this question, then the root cause of why he went to gambling after all the years of quitting might have been half resolved.
More work needs to be done after quitting any addiction because the kind of company you keep or hang out with, either in the workplace or living environment might make you fall back to same sin you just escaped and that's a reality many face when it comes to certain addictions like gambling activities.