No real advice, other than to say I'm going through similar.
Recently my ex ended things, haven't blocked each other or deleted off social media as it ended "nicely".
I have muted his posts and stories, and put him in my archive folder on WhatsApp (you've done better than me by deleting! 👏). However, I have gone into my insta dms to reply to messages, I don't have a lot of friends I speak to on there so he was still coming up near the top of my recent chats. I've noticed every day since the break up he has been posting stories, I haven't watched them but I can see he has them on.
It's honestly made me feel the same way, he's off living his life and posting stories (must be out and about doing things), meanwhile I'm here crying my heart out barely able to function. He rarely ever posts on instagram let alone stories so it's really bothered me, even though I know it isn't my business anymore.
Like others have said, he could have checked out long ago and just relieved to be getting on with his life.
He could also be feeling sad and be masking the pain and putting on a front. My ex ended things with me once before and did similar behaviour, when we got back together he did state this as the reason.
At the end of the day, you won't get inside his head. It is going to hurt, don't block it out and accept your emotions. You're allowed to feel hurt, you're allowed to feel sad. Especially if you've been blindsided and he was good at pretending that everything was great.
Ask friends to stop updating you, and resist the urge to check yourself. The next few weeks will be hard, but after that it should get better, slowly. It's like a withdrawal. You will only cause yourself more pain by thinking about his happiness, whether it's real or fake.
You've got this x