@Tannith,
First thing I will say is that I am sorry you seem so anxious, and alone. The anxiety, I understand. If, like I did, you got a letter telling you you were at great risk, and needed to avoid all human contact for at least 3 months, even to the point of preparing meals separately to anyone else in your household and then go and close yourself in a room, on your own, to eat and spend the rest of your time, then it is hardly surprising that anxiety is through the roof. It is difficult enough coping with the ailments that make you vulnerable, without the added angst of isolating.
As others have mentioned, there are ways to get food delivered from supermarkets, and/or independent retailers. Most, (apart from supermarkets) are fighting to stay in business, and desperate to deliver food to you.
For some reason, I seemed to have been missed off the shielding list Government sent to supermarkets, despite having letters and texts telling me how vulnerable I am and that I must follow the shielding guidelines. Had I been waiting for the food boxes, and emails from supermarkets I would be somewhat emaciated by now. I phoned the local supermarket and at first they said they couldn’t give me priority slots, until I mentioned that they would have record of my previous purchases, through their loyalty card scheme, and could see how much I spent weekly over a number of years, and that I hadn’t been in there since the start of lockdown. They did give me access after that. I use them to buy things that I can’t get from the independent deli / restaurant, which diversified in order not to go out of business. They deliver. They win, but so do I. Also, just this week, Co-op emailed. If you have membership card, which costs £1.00, the local store will accept email orders, for delivery, usually the same day. The selection of items is less varied than most supermarkets, but essential items are available.
I am not sure where you live, but local councils have been tasked with providing help with shopping for food and medicines, or other assistance vulnerable, shielding, folks need. Perhaps you could contact your local council to request help from the service they provide?
Regarding staying in my home, shielding for evermore, it is not going to happen. I want to really live, not merely exist. The way I look at it is that early on in this pandemic, there was a group of snipers outside my front door, waiting to fire at me if I so much as peeped outside. Some of them have been eliminated. Most have moved away. So I have to remain vigilant. For now that means avoiding areas where lots of people are. Or, for now, even a few people, even those I love outside of my household. My self preservation strategies will change as circumstances become less risky, (if the metaphorical snipers seem to be under arrest) or if there seems to be an increase in risks, (like the snipers have recruited others) . What that will take is to be aware of who is around me, where I choose to go, and what the news and media are telling me about the levels of infection in places I want to go. Then I will make my own, calculated risk assessments.
I really hope you can find peace with it all, Tannith, because the alternative is to stay hidden from the world and very lonely. That is not something I would wish for anyone.