At one time, this fandom meant the world to me. I'm grateful for all my experiences as a beta, both good and bad. Whether you see it coming or not, a writer can wave their hand and decide to banish you to the sidelines.
It doesn't matter how many hours you put in either editing, looking up words, and rearranging sentences, while trying to make THEM look good.
It doesn't matter how many late-night frantic private messages you get questioning plot choices or character development. It doesn't matter that you helped edit fan fiction stories into published stories, only to be forgotten when they went live. Oh, and how about this little gem: finding out you were replaced when they published a chapter and somebody else is listed as the beta, and they didn't have the courtesy to tell you. Talk about public embarrassment!
The bottom line is no matter how much you help a writer, it's their story; you were just a means to accomplish their goals, and really meant nothing to them. Expect to hear these phrases: "It's not personal!" "It's my story and I can do whatever I want!" "I'd like us to still be friends!" "I do hope you'll still read my story and review!"
This is why I chose to hang up my beta cap, throw away all my red pencils, and stop reading fan fiction.