There really isn't anything you can do to make someone be more comfortable with you and let you into their lives, he either wants to let you in or he doesn't.
He's 25 years into recovery, at this point he should have a solid plan of recovery and he should have a good handle on how he wants relationships and friendships to work. Granted, some people can be sober for 25 years and not work any plan of recovery and not be in any better place then someone that is a year into recovery, either way you can't make him open up to you.
I would probally talk to him about your feelings. I would just watch directing the convorsation in the direction of "You won't open up to me because you are in recovery", because quite frankly, taking these relationship problems and saying they are because someone is in recovery could be taking it out of context and be really insulting. At 25 years sober he is most likely not incapable of having strong relationships and being open.
I don't mean for this comment to seem rude or harsh, I just think that you need to treat this as any other relationship you had when it comes to the issue of him not opening up to you. As for the gambling, well gambling is addictive and can cause people to lose everything they have. As I said before, the best thing you could do is talk to your boyfriend.
Communication is usually the best way to figure out where you stand in a relationship and if there is a gambling problem manifesting.