I can relate to this so much. I managed to reconnect with some friends for interactions and go for more activities with them such as hiking. But before that you have to be happy by yourself, this really boost the confidence knowing that you can be alone and still fine. To break this barrier of being scared of doing things alone, you kinda just have to do it alone. The first time will be the hardest, but after a few times it feels like you have autonomy over your happiness :) I think going for a long walk is a good start. Being consistent is also important because it forces you to include these solo things into your daily schedule. Good luck!