You're his friend, he has a new girlfriend, and he figured you wouldn't mind driving around and helping him out with the calling bit (that's my guess). If it really bothers you that much, then I'd let him know. However, it's not as though he's ditching you for her; anytime anyone starts a new relationship (whether or not they're you're very close friend), they're gonna be a bit more scarce than usual for the first few months.
Besides, he can only talk to his girlfriend at time X; he can see and talk to you whenever.