Here was my note for my s/o before I missed my date and plans had to change. Maybe you can draw some inspiration, but bear in mind that this will be the last piece of you your loved ones will have left, your parting words. Even if they're not the most eloquent words, it's important that they're in your voice so to speak, so as long as you speak from the heart you'll be golden.
You're an extremely perceptive man, one of the many traits I've come to adore in you over the years, so I'm sure you already understand the nature of this note. Please DO NOT look for me, that isn't something you need. I'm in the room but I've hidden specifically so that you don't have to see something traumatic. By the time you read this, hours will have passed since I took my intended course of action, there will be nothing to gain from looking for me yourself. Please abide by my last wishes and call 911. Wait outside for them. They'll know what to do.
I'm not sure how legally binding something like this is, but if it is I'd prefer to entrust the deposition of my remains to you. I'd ideally like to be cremated, and you can do what you like with what's left, but I'd prefer it if my family had as little to do with this as possible because honestly they don't deserve it. Don't bother with a funeral, that's an expense nobody is prepared to handle.
Please understand that my decision to do this had nothing to do with you or anyone else, it's been the plan for many years now. It's just that my strength has finally run out, and I need to rest now. If there's a life after this one, I'll still be here to guide you and look after you. Don't feel like I've left you behind because I haven't, I'm just on the other side of the veil so to speak. This isn't for lack of love for you, I loved you as much as a human is capable of loving another, and will continue to do so. Death won't take the things we had from either of us. I'm so so sorry that I let you get attached to my physical being, I still understand that loss I'm imposing upon you, but please keep our memories close to your heart and there I'll continue to live. Until our next life, goodbye, and I loved you so.