They are probably just as jealous of you.

The person your jealous of, Weather its your best friends girlfriend,your boyfriend/girlfriend,friend. They are probably just as jealous as you.
If your jealous of your best friends girlfriend then you need to realise that the girlfriend is probably jealous of you too. Why wouldnt they be? You are best friends with their boyfriend and you will always be in his life because you are best friends, weather as they could break up and never see eachother again. This can count for most things to,changing a few things.