I understand how you feel and empathize with you. I believe that you were simply being a good mom in wanting to drive your son to his girlfriend's house, rather than let him ride his bike over in the dark. In this day and age, I don't consider this over-protective, unless the girl just lives down the street.
However, you need to understand that your son sees things differently. He's growing up and after all, he seems quite responsible. He's doing well in school and even has the sense to find a girlfriend who treats him right and shares a similar work ethic with regard to school.
I don't think your son is pushing you away as much as he's trying to exert some independence and asking you to honor his privacy, especially with regard to his first boy-girl relationship. He is honest enough to admit to you that he is new at this and feels uncomfortable discussing this with you, so let him have his feelings. As a mom, I would be pleased that my son trusted me so much and was so articulate that he could express his feelings so clearly.
While I understand that you feel hurt, know that as he starts to feel more comfortable with his relationship and all the feelings it entails, he will share some of his thoughts and questions.
Just let him know that you're there for him. Tell him that he's growing into a fine young man and you're proud of him and pleased that you can trust him. But do let him know that if he wants to go to anyone's house after dark that is x distance from your home, regardless of whether it is friend or girlfriend, it is your job to make sure he gets there safely.
