If you won a day at a spa, you would be able to spend that day virtually alone with your body.
No phone, no people, just you getting that soak, that massage, that mani/pedi, etc.
Take a day… half a day… shut off the phone, and take a hot bath or whatever, and just spend the next few hours looking after your body; do exercises, pamper yourself, just you.
If you can do it for at least four hours once a week you can begin to build up that self confidence, that home inside yourself which will make being alone not lonely.
Just try to be alone with yourself, you will find how it matters in real life.