Methadone is taking over for Oxycontin and Oxycodone as the hot new legitimate med gone bad. Frequently prescribed for both acute and chronic pain, it is in such demand on the street that ordinary people with jobs and homes and families get sucked into misusing it, buying it illegally, and, something they could never imagine beforehand, selling it. This is happening in respectable neighborhoods all over suburban and rural America.
Unlike meth users, who become visibly ravaged in a comparetively short amount of time, methadone addicts can remain relatively normal in appearance and function for years. And because a great many of them begin this downward journey with a legitimate prescription, they can rationalize their use in such a way that they truly don't believe they're doing anything seriously wrong.
The most important thing you can do for yourself, your sister, and the rest of your family, is to learn all you can about this insidious addiction AND how to set the boundaries you will need to keep from getting sucked into the co-dependent game-playing that addicts so heavily rely on to keep their house of cards intact. You can Google Nar-Anon, a support group for families and friends of addicts, to find resources in your area.
If there is no Nar-Anon group, Al-Anon may be the next best thing. The drug of choice may be different, but addictive thinking and behavior and the manipulation and deception they employ are the same.
You, and anyone else interested in helping your sister, need to educate yourselves with solid information and arm yourselves with planning and resolve to avoid becoming ensnared by the emotional ploys and pitiful pleadings of a person who will do whatever it takes to maintain the status quo. Your sister isn't evil, but addicts will redefine good and try to justify committing outrageous acts of selfishness and destruction to get the drugs they crave. It's the nature of the disease. Unfortunately, they learn to exploit the very love that keeps people attached to them until they burn it out or drag others down with them. It's not a pretty sight.
You can't force your sister to accept help she does not want. What you CAN do is develop an awareness of addictive behavior and fortify yourself against her attempts to use and abuse your relationship. You can learn to ditch the false guilt that addicts can smell from miles away and will use against you in a flash. You can come up with a game plan that helps you to stay connected without being sucked into the drama. As long as she (or enabling others) can somehow make her life work, she will not allow herself to see how much she needs the kind of help that involves getting clean and becoming honest.
As tempting as it might be, don't give her indecent proposal a big emotional reaction. Provoking others is a fairly dependable method of keeping people hopping and distracting them from the real issues. If she were in her right mind, she wouldn't need to rattle your cage OR borrow your husband. When she comes up with loony ideas or brazen requests ("Can I borrow $1000?" for a down payment on a car with monthly payments she can't afford), give her a simple, low-key response such as, "No, that won't be happening," and move on to another subject. This robs her of your emotional melt-down and the chance to knock you off balance. And it allows you to think instead of feel when dealing with nonsense.
None of this is easy. But neither is it easy to keep getting sucked in and going along on the terrible roller coaster ride.
I'm so very sorry about the loss of your other sister. Please sort through your feelings about her death and discard anything that holds you personally responsible. Suicide is a choice made only by the person who commits it. If you haven't gotten any counseling or therapy to help you get through this, now might be a really good time to pursue those options. Otherwise, you could very easily merge your sisters and imagine, on an emotional level, that you can save the one by continuing to rescue the other, a state of mind that will make you ripe for exploitation.
Please, talk to other friends and family members (in a support group) who have an addicted loved one and learn from their experience. Let them offer you knowledgeable support and encourage you to become strong and protected.
Find solace in a group who will know without needing much explanation what you are going through and who will be there for you in sorrow or in joy.
Take very good care of yourself. Set a good example that your sister might one day be able to follow if she chooses recovery. And remember, you can't save her, but you can save yourself so you will be there when she's ready for genuine help and acceptance.
She's blessed to have you.