<human>: Could you distill the essence of the text into 1-3 sentences?

I am a 20 year old guy and I just entered a relationship with a girl the same age. She is my first girlfriend and I am her second boyfriend. We had rough patches before we entered the relationship because we both experienced heartaches in the past. Mostly it was doubt from us both, and we were both scared about entering a relationship.

She had a bad break up (with her first boyfriend), and because of that she was afraid of going into another relationship, this was according to her closest friends and her too. That is all I know of her previous relationship, I'm not one to go prying into someone's past, I don't care about that. 

I on the other hand, was single up to when we entered our relationship, but I was kept on the hook by the girl I was previously courting, this was four years ago before I met my girlfriend, and I moved on from that girl completely.

At first when we entered our relationship (less than a month ago) we were happy as can be... Lately she has been jealous of the girl that I was previously courting before her, even though I told her again and again that I moved on from that a long time ago. She just won't believe me I don't know why... I think its the doubt that she first experienced when I was courting her...

Any advice would be appreciated, Thanks Guys and Gals...
<bot>: I [20 M] am new to relationships (first time) and I don't understand why my girlfriend [20 F] won't believe that I moved on from the past girl I was courting...