People Who Expect Me to Be Nice to Them when They’re Mean to Me

My ex-friend has done a lot of mean and rude stuff the past three years. Whenever she does something and we confront her she’s always like, “I’m so sorry!” Or “I’m sorry x10000!” And we forgive her, but then she does it all again and each time expects us to forgive her and be nice. I know that ultimately we should be the better person, but after this long of it going on, I don’t want to anymore.