Apparently we can all manage to maintain a relationship with around 150 friends. It's called Dunbar's Number, after the scientist who identified it. Actually, it's not an exact number , and could lie anywhere between 100 and 230, but that doesn't matter. The point is that it's finite. We're talking here about proper friends, people you can have a meaningful relationship with, who you can interact with. As you go through life you meet new people. Some of them you like more then others. It's normal. So work to keep the friends that you really want to hang on to, but don't feel bad when others drift away
Sometimes you got to cut and move on.
Some of us can mantain even more.