My brother was a terrible alcoholic and drug attic.
He was in rehab, did the 12 step program and went to meetings frum, he was clean - clean! for almost 3 full years, went to LAS for a little vacation (he wasn't a gamble addict) made a few bucks so of course made a little le'chiam, the end....
First of all, I'm sorry for your loss. Hashem should give you and your family the strength to deal with this terrible tragedy.
Next, I ask, why "of course".
Without judging him, he may not have been a gambling addict, but the casino is an open and free bar...not a place for a recovering alcoholic.
Finally, I say, many times we see addicts stop one addiction and trade it for another. Its like a balloon. You push it in in one place and it comes out elsewhere. 12 step programs are designed to stop addictive behavior by bringing about a progressive character change in the addict. Change in the way the void is filled. Change in the way one deals with crisis. Change in the need to escape reality and deal with real life issues.