It sounds like you are just insecure, you don't feel good in your own skin, I think it has little to do with that other girl that you feel jealous off. What can you do to stop it? Find a way to like yourself for who you are. Do something good for others, do things that you believe a respectworthy person would do, so you will start to respect yourself.
Don't cry, don't regret and don't blame
Weak find the whip, willing find freedom
Towards the sun, carry your name
In warm hands you are given
Ask the wind for the way
Uncertainty's gone, your path will unravel
Accept all as it is and do not blame
God or the Devil
~Born to Live - Mavrik~