Pugs,
I think it is courageous of you to learn to say no. I have to remind myself from time to time that no is a complete sentence, needing no explanation.
I find your post very insightful because I love someone with depression and they are doing the same. I am trying to understand their perspective and you explained it well. Thank you!
It can be difficult for your friend to understand the pain and struggle to heal. You may want to try to express it to them the best they can but you should not feel bad for saying no and taking care of yourself. Maybe explain you would love to meet with them but are not comfortable in a certain setting and offer an alternative you are able to manage. I have a dear friend that is in a similar situation and from time to time she just tells me she cannot buts want the company and I advocate the best I can to ensure the plans are changed and if not, I will bow out too and have a quiet evening with her.
Be patient with yourself and focus on those that understand.
Good luck with your healing!