I'm so sorry you are in this situation. It was nearly 3 years ago I got the I love you but not in love with you speech. My world fell apart. He spent six months telling me he didn't know what he wanted (obviously ow on scene of course) before he left for good
Your kids will be fine. Mine adjusted quickly. It took me a long time to catch up.
He is no longer your friend. He will lie to make himself look and feel better about the situation. Time to cut him off.
Sit down together a tell the children this weekend. They are old enough to be grown up about it. Dad doesn't love mum anymore and sometimes things don't work out. He is moving out. Then he goes.
Pack what stuff you can and get his belongings out of your way move things around at home. Get new bedding and flowers. Just change things around a bit. It helps.
Gather good people around you. Family and friends. Seek support from your gp and counselling to get your thoughts out. I use to write draft e mails. But not send them. If you need to communicate. Don't respond right away. Write something and sit on it for an hour. Or over night. Don't communicate when you are feeling emotional.
Legal advice and CMS. Get your ducks in a row. Show him you are taking control of this situation now. And arrange contact. Obviously lock down is making things harder. But he can take the children every Sunday for example.
Look after yourself. Eat when you can And just get through each day how ever that looks. If it is tv and pasta so be it. This will pass and in time you feel feel less sad.
If it helps my ex at the beginning of lock down surfaces in a mess telling me the grass wasn't greener. It was just different grass. And he wished he tried harder. 🙄.