Which is a perfectly reasonable way for someone to feel

Yeah, sure it is. But here is the point everybody here is complaining about... when that is the case, you talk with that person.

Do you expect a formal note listing the reasons why she doesn't want to hang out anymore? That's not how society works.

After being friends for half a year? Yes, I expect her to talk about it and not just going silent from one day to the next, and letting me figure it out over the course of the next 2 months while she always says "Sorry, I have already plans! I have time starting next week!" only to get a "Sorry, I already have plans!" again and so on, and so on. Don't you see that the exact problem of all of this is, that people think they don't need to talk to anybody and can just vanish without a comment? That is what makes it disgusting. Leaving people behind, wondering what is suddenly up.

it's her life and she can do whatever the fuck she wants, it's none of your business.

Sure she can. But not even thinking about how she might hurt others makes her an asshole. Seriously not even getting why I get shit for this opinion, when everybody else in this topic here complains about the very same thing and gets upvoted... Heck: The post itself is about exactly this and got 13k upvotes... but somehow I am wrong for being angry about people acting like this?