Emotional detachment is a complex and very hard thing to do. Some people are naturals when it comes to "Letting go" of people. One of the main things I've confronted in life is how easily people will move on without you. To you, they're your whole life, but to them you're just another name in a contacts list.
One thing you can do is analyze why you care so much about them, or their opinions or how they'll feel. Do you honestly believe they'll miss you? For how long? At what point will they move on? Do you think they'll change?
Think of all the people who've ghosted you, for example. In your life, how many people have you become attached to who have cut you off without so much as a goodbye? Things will continue spinning after we're gone. Some people get their names on benches, but how many people stop to read it? would it matter?
I'm not saying you should, or that you can, but letting go of all the things that you will miss is a hard thing, because part of you wants to miss them. They're things you attach meaning to, and when you're gone, that meaning is gone as well.
Before you pursue this, though, I'd suggest maybe exploring the source of your pain first. Maybe something is missing that you can find, or maybe something is there that shouldn't be. That's one reason I bring up analyzing why you would 'miss' things. Why? What does it bring to your life? Is it goodness? Or bad? Should it be something you miss? or can you do better without it