Hello butterbun. I can empathise with your feelings. Time was I would wear my best outfits to engagement parties, weddings, even the odd christening. Now I wear them to funerals. As old age creeps up on us we are reminded every day of the things we have difficulty in doing, if we can do them at all.
However, there still are many pleasures in life to enjoy. I suspect this heavy feeling you have now will pass somewhat, especially when Spring comes about. It has been a long winter for many. For the sake of your lost friend continue to laugh and enjoy the parts of life that you can. She sounds like a lovely person and you could do far worse than to make your life a tribute to her whenever and wherever you can.
Remember, life is for the living and we all need to grab precious happiness at every opportunity. Best wishes to you :)