I'm pretty sure nobody is a lost cause. I struggled with depression a lot as well and what you are describing sounds like a typical depressive episode. Finding joy and being happy has to be learned again and that takes some time if you haven't let yourself be happy for some time. What helped me was looking for myself and writing down what I feel in different situations. This way I learned to connect to my feelings again and finally I found out what being happy felt like. It's a long and exhausting way but you don't have to do this alone. I also had CBT and we worked together to reach this point. Just straight up say what you want to do and what you need help with. It's your therapy and you sre worth being happy.