My boyfriends ex still has feelings for him?

Honestly its not as bad as it was in the beginning of our relationship. We have been dating for a little over a year. His ex; lets just say her name was sarah, still likes him when they only had dated from sep-dec of 2009. Ive known 'sarah' since middle school and then when it was our freshman year she got a boyfriend named joey(my bf now) they only lasted like 3 months and then he broke up with her. I don't go to the same school but joey started talking to my best friend a month after breaking up with sarah. When my best friend came to my house for a sleep over, we went to the mall to hang out with joey. Things didn't work out with them cause my friend wasn't interested anymore, Joey was upset so i talked to him on the phone to give advice. Eventually he fell for me, we hung out alot and 'sarah' got pissed at me like i stole him away. I never took him away he wanted someone new and that was me. When we started dating in May she tried alot to break us up, and almost did a few times. She eventually gave up trying to win him back, but she still likes him and she told me this. She always texts him and says there random little memories from their 3 month relationship. It has been annoying me and i want her to get over him cause he doesn't wanna be with her ever again and he told me this. Whats it gonna take for her to get over him, i don't know what keeps her hopes up about it.. help?