Scared of losing him

I have been with my boyfriend for 5 years now. And I'm going to be living closer to my school next fall. He just told me he is going to get a drive to his school and his work from this girl (because they work and starting go to school together next fall), he specifically said "she is buying a car for us." So it kinda pissed me off. So they will be spending a lot of time together. And I wont be seeing him as much as she is. And I am scared she may start to like him.... he is a great guy. And he may like her. I trust him but I don't want to lose him. At the same time maybe its okay if we see other people because we have been together since grade 9 so.. I don't know what to do. Any advice?