I'm going to tell someone I didn't want to be lifelong friends / can't handle the intensity of our friendship
That's unfortunate. Why don't you want to be lifelong friends anymore?
I don't think I can handle the intensity of our friendship anymore. It's just too much for me to handle.
I'm sorry you're not feeling well about the relationship, but they are very enthusiastic about you are you are going to crush their hopes badly by rejecting them. You just need to tell them to tone it down for a while and understand how you feel about it all.
I dont have time to take care of everyone's feelings. They are not a puppy that I need to pet.
It's definitely not your responsibility to be there for everyone, but it would still be nice to stay friends with everyone, right? How would they feel if their really good friend suddenly rejected them? Why not just talk to them and tell them they can save their energy for more appropriate places?