The way you deal with jealousy is to work on making yourself into someone who is worthy of good things by going to school, helping others, getting a good job...when you feel good about yourself, it's easier to deal with another person not treating you well. It's their loss, because I'm a good and worthy person. There's alot of good people in the world, and if you don't want to be true to me, I'll find someone who will.
To deal with jealousy you should look at the object of your jealousy from another angle and avoid stressing over what you cannot control. If they like each other, try to be happy for them. You should also avoid them at all cost.