Should i try to get her back?

my girlfriend broke up with me about a month ago, things din't really work out. her friend apparently had a crush on me too and in order to preserve her friendship she broke up with me for her friend. now everything is messed up. anyways, i haven't talked to her for months. but a few days ago it was my birthday and out of the blue she text me a happy birthday text message as if we were still friends and nothing happened. i kind of answered back in a cordial manner and kidded around with her. i still like her, but it has been so many months, maybe i might meet someone like her if i give up this chance, but what if i don't? i am uncertain about what to do now. what is her agenda?