I'm so sorry - a broken heart is a horrible thing, especially at the moment. I split with my BF during the lockdown as well. Things I've found helpful - keep busy - don't allow your brain the space to think about him. I've scraped wallpaper, washed down woodwork, done loads of small DIY jobs, worked in the garden and painted anything that wasn't moving.
I also read a booked called Its Called a Breakup because it's broken. (£2.99 on kindle download). It's a bit of a harsh read, but it was what I needed. I was very guilty of looking at the relationship through rose tinted glasses. He wasn't the great guy I thought he was, I made excuses for his behaviour. I deserved a lot better and I will get it. The breakup has allowed me that possibility now.
Don't drink or eat too much- you will feel worse as you pile on the pints and wake up with a fuzzy head - plus you're more likely to make a phone call you regret (the book has some v. good advice on this). Care about yourself like you were looking after a friend.
Of course you will miss him, he was a huge part of your life. There was also a time in your life when he was not in it and you managed perfectly well then. Its natural to want back what we had, the familiarity, the comfort, the security of it. You feel lost and not sure what to do next, you have no road map of there you are going. Except you do. I try and look on the relationship as a chapter in my book of life. I wanted it to be the last chapter, but it's not going to be, however much I want that. So I can wallow for the next few months, picking myself apart and wondering how I can get that man back, or I can take a deep breath, draw a line under it and accept its over.
Its sucks big time, and the early days just feel like ground hog day, but you'll get there. One day you will wake up and he won't be the first thing you think of, I promise.