I was thinking about what you were saying about methodone maintenance. Usually I would advise anyone to try their best to avoid taking the MM route, if another way could be found, simply for the fact that the half life is so long, making withdrawals a living HELL, or so I have heard over and over again (Have never been on MM). Subs are another option for maintenance.
But, your circumstances are a bit more urgent. You have so much on your plate already. Caregiving is known to be an exhausting job. Add to that fact your love for him, and your fear of losing him, and you have a recipe for dropping from exhaustion, stress, pain, anguish, etc.
The last thing you need during this difficult time in your lives is to be in withdrawal half the time, trying to cop, trying to resist the temptation that him being scripted so many opiates brings.
Going through withdrawal while caring for him and spending your precious time together...you just don't need that added nightmare.
If I were you, I would look into some kind of maintenance program. Get you removed from the lifestyle of copping and being sick while you are already straining to provide for his needs and comfort.
I don't know how this would work, but perhaps there would be a way to, when and if you need to get off maintenance and you were taking methadone, maybe you could switch at that point to subs which if I am recalling right, still has a long half life but shorter than methadone. And it is fairly easy to cut down and taper off of subs....technically, of course.
But honestly....you can worry about that later. I don't think "worry about it later" is a good OVERALL way to live life. However, some intense and urgent and incredibly stressful times in life require a fast solution to a current problem because the cost is too high to continue that way, and once things settle you can work out any issues with said chosen fast solution.
I would get on Google and search for someone to help you do that.
Big hugs hon.
Peace.