I'm not sure that we have met .. so welcome to the forum!!!
Oh Hon, I KNOW what you're going through, my husband can't drive because he's legally blind & he can't pass the eye test. So, he relies on my to get him everywhere. If I'm a minute or two late I always feel terrible. Last fall, when I was still working, I forgot to pick him up... I completely spaced it. When I finally realized that I had forgotten him I jumped in the car and sped to his work and he wasn't there. A friend drove him home while I was on my way to get him. So when I got home he was extremely upset with me. After he grumbled at me for a while, I finally said, "I feel so bad about forgetting you, I was completely overloaded at work and time got away from me. I really didn't mean to forget. Please, I feel bad enough about this and all of your whining isn't making me feel any worse than I already feel." By the next day he had gotten over it. But I still feel bad about it till today.
Tyno mentioned checkinng out Fibro 101, the second thread on the forum.. there are lots of links on there that can help when you're going through a tough time with people in your life that don't understand fibro and how it effects you.
I hope my story helped you a little bit. Don't be too hard on yourself.. we all make mistakes sometimes.. with or without fibro.
Take care and gentle hug,