I'm truly sorry that your friend of 20+ years isn't supportive of you and your decision. The only person that I've told is my husband. He's attended dr. visits with me. He's VERY supportive. It's most helpful for me to have one person that loves me and that I trust to discuss this huge decision with. I have discussed everything with him: my fears, anxiety, shame, etc.
Hopefully, your friend will have some time to process the information you shared with her and begin to support you. You are an adult woman that can make your own informed decisions. You do not have to justify your decision to her. Only to yourself. Perhaps you can invite her to join you at one of your clinic visits so that she can learn how to better support you. If she cannot support your decision (I hate to say this...) but just how good of a friend is she being to you? (sorry if that stings)
I know that some people on this forum are able to sing to the rafters the news of their decision to have WLS. I respect that in them. I will not tell anyone else until after the surgery - if then. I will need to be off work but I will only say that I'm taking vacation. I may feel differently after surgery about sharing my decision to have WLS but for now, I'm keeping my decision to myself.