Are ex girlfriends naturally jealous?

Soon as my boyfriend's (now my husband) ex-girlfriend knew that we dated, I began to receive pictures of him and his ex when they were dating (of course before I ever knew him) from unknown email address. Then as we were soon to be married, I received IMs using yahoo IDs I never knew, warning me not to marry my husband telling me that he was already married before. My husband also received IM from this same yahoo ID telling him he should not marry me since my reason of marrying him was because I just want to be near with somebody I truly love in the US, since I lived in another country. His ex girlfriend also keeps posting their past pictures in the internet. It took her 3 years continuing to bother us, and she still is. How come she is this so jealous? If not, why do you think she is doing this?