What's "fail" mean when it's used for a person like here?

Native speaker’s answer
Rebecca
To "fail someone" means to disappoint someone by not meeting their expectations or betraying their trust. Here, she is saying that she recognizes that she disappointed her ex-lover, that she betrayed his expectations or trust. Ex: I'm sorry I failed you. I'll do better next time. Ex: He failed his business partner by going behind his back to make deals.