Well what if you DIDN'T have a crush on this friend? Would you be worrying about being left out or that you'd be left?
I would just suggest that you shelve the fact you have an unrequited crush on the person, and do all the normal things to work on your jealousy. It also sounds a lot more like envy than jealousy. I'd keep busy and not spend time with the crush until my feelings had faded, but that's just me.
Happiness will never come to those who fail to appreciate what they already have.