I have tried filling the void left by opioids with different hobbies, meditation, relationship etc. but still I relapse in some point and the trigger is often the boredom or feeling of not accepting the reality of having no real reason to live or no part in the big picture (ie. in scale of universum). I could even say that in the worst times using opioids along with benzos is an alternative for suicide.
I think this is really just seeing human life for what it is--our crazy, lonely, personal journey with our human minds. Dogs don't need the bigger picture and neither do snakes or birds or elephants but man, we sure do. We want to feel meaning and understanding. We want the thrill of being launched out of our small lives into something that we perceive to be there but cannot see. We want the peace of letting the burden of our ego's insatiable desires lifted by feeling our place in the grand scheme of things. But most of us stumble in and out of all sorts of ridiculous and self-defeating things because on the one hand we are these marvelous thinkers and have the imagination to grasp that there is a bigger picture and yet on the other hand we are simply complex bodies playing out whatever roles we have accepted from our tribe's cultural edicts. Some people get in bad relationships, some people buy things they don't need, some people eat and eat and eat and some people struggle with drug addiction but it's only drug addiction that gets the bad rap and the stigma.
As far as the boredom being a trigger, I think the best antidote is travel. My son just got home from hitchhiking around Central America for a couple of months and he said that he is trying hard to hang on to that feeling of pleasure that just comes from observing as well as the excitement you feel when everything is new and uncharted. It's easy and natural to get that when everything is exotic to you but when you come home it can also help you to not fall back into routine and boredom by reminding you that even where you live there is pleasure to be found in people watching, trying new foods, interacting with strangers openly etc. Are you still planning on taking your U.S. trip?
I think you would like the author, Craig Childs. He's a naturalist adventurer and his latest book, Apocalyptic Planet, draws your mind out of the small and into the scope of geologic time. He has a knack for understanding the here-and-now miracles we are surrounded by and the total irrelevance of all of that on the grand scale. I don't know if it would speak to your sense of a "reason to live" but it did speak to mine. Basically it just takes the burden of having
any reason at all out of the thought process. In other words, you are here, it won't last long, open your eyes to what is around you and dig it while you can. I don't believe there is any reason for us to stay alive, there is only the desire to do so and the uniquely human connections we make with others, with other species and everything else we encounter along the way that make it worthwhile.