I have been struggling with this same question myself. How do I slowly acclimate those I love to the eventual reality of my absence? How do I let them know that I don't want to hurt them, only make their lives better? Well, that, and, of course, escape the horrors and shackles of my own mind.
What people too often don't realize is that, for many of us, suicide isn't really a choice. When you struggle with mental illnesses that keep weighing you down more and more, dragging you further into the dark abyss every day, happiness ceases to be an option. You remember what it was like when you could still truly feel it, all those years ago, and you try to fake it for others' sakes--or maybe even in the desperate hope that if you try hard enough you'll actually be happy again. It doesn't work, of course; the illness has progressed too far and that part of your brain is too jacked up.
So, suicide isn't truly a choice. For some of us, it is the inevitable end. It was always the way we were meant to go, from the very start. But, even knowing that, how can we prepare our families and friends? Because, although we may have little more control over suicide due to mental illness than, say, a cancer patient would have over their own deadly sickness, other people don't see it that way.
If someone has cancer, experts advise that they speak to their loved ones, gently but openly, helping them mentally prepare. They recommend spending time with those you love, making final memories they can cherish, and enjoying your last years or months together. When the thing that is going to kill you is not cancer but rather your own brain, that isn't really an option. You can't tell people that you are going to die from suicide, that you are holding on as long as you can for them, but you don't think you can manage it much longer. They'll make a scene, pressure you into calling the (utterly useless) suicide helpline, try to guilt trip you into wanting to live. Or they'll turn it into a fight, really bring on the dramatics, start trying to belittle your emotions by playing "Compare the Trauma." Just because you love someone doesn't mean you can trust them with your feelings.
So how do we help people we love prepare for our final exit when we can't talk to them? I mean, obviously, they'll get notes saying goodbye afterward, but that doesn't really lesson the shock, does it? How can we prepare them beforehand when we have to keep our hearts a secret?