A lot of people have a work persona, which may account for how your friend changes when she’s around the manager.
I also took note of your fear that your friend will “leave you.” What does this even mean? Your friend is allowed to be close to multiple people at the same time. As are you! Do you have other close relationships? If not, is that why you’re so concerned with the interpersonal relationships of others at work? It also struck me that you feel your friend tries to make you jealous, which doesn’t sound like a good friend to me.
Maybe the manager doesn’t ring you because they have more confidence in your ability and don’t feel as much of a need to check in?
Work is work and it’s a great skill to learn to leave it behind as much as you are able when you go home at night.