Marie, welcome to SR.
You will find a huge amount of experience, strength and support here. I understand what you are going through and so will almost everyone here because we either have or are going through it.
I've lost my best friend also. She just kind of slipped away over the last 13 years until it felt like I was living with a stranger. I also lost myself for a lot of that time trying to help, fix, cure her. I now accept that I can't do that and have started to work on fixing me.
You will find a lot of support here helping you to fix you. Which of course is all you can really do.
Best wishes and prayers to you on the start of this new adventure. The results are worth it.
Your friend,