has been my only friend for this whole time<--This is hurting you. With good friends, comes strength and support. Now I know you like people. I bet a lot of people like you! So get out there, call old friends, make new friends, join al anon if you want to meet people who understand what alcoholism did to you, join a book club, a health club, a cooking class, a film buff group, a gardening group--what are your interests?
You need friends, and they are good for you!
Stop isolating. Stop robbing yourself of enjoying life and friendships. That's part of getting mentally healthy again, moving on beyond him, and finding joy in life again. It's all good for you! It's difficult to create a life again, it feels tough especially at the beginning, but you can do it. With friendships you won't feel such panic because you will have other people that bring joy to your life. Then this one person isn't so important, and over time will become not important at all !