I live on my own and have done for years. So you get used to it and find inner resources and there is so much to do in life alone or not. I rarely see adult sons now for valid, various reasons. 2 'friends' took advantage of the pandemic to isolate and then move house...without telling people! That hurt. Other old friends have passed away/remarried/moved away.
I have also just extricated myself from a 'friend' who was being emotionally abusive and I just couldn't take any more. So very alone. But it had to be done. Recovering at the moment.
I have a lot of interests, walk a lot, and have an agenda for the week to keep me busy and in a bit of a routine. So try not to have too much time to think and get low. I have a plan/something to see to every morning/afternoon/evening. At weekends I stay close to home, the world and traffic is mad then anyway [and full of couples and families]. I'll do stuff in the house, choose good tv/catch up, you tube/forums, walks, reading, gardening, baking, cook nice meals, DIY, puzzles, drawing, long baths, shop locally etc.
I know it's hard, especially if you aren't used to it. I have faith though, that things will change and every day is a new start to the rest of your life so I'm optimistic most of the time and like my own company though I have a great sense of humour and love laughing.
I was an only child for my first 11 years though and I learnt to rely on my own company then, and it set me up well. I also witnessed my grandmother who was very alone, very stoic but made the most of every day so I had a great role model there. If fate says I am as dignified with solitude as she was then it's fine with me.