What your parents are doing sounds worse than normal to me.

Your father's comment about 'Well, we aren't doing anything on my birthday' is an attempt to guilt you into visiting on the 4th (and it sounds like they don't do anything then, either). When my mother throws guilt trips like that on me, I either ignore them or turn them to my advantage.

That crack about not doing anything on the birthday? I would say "Oh, so you don't want me to come down? I guess I can work instead." That's probably passive aggressive in some way, but parents who refuse to let go of their children, who demand excessive contact and then guilt the kid when that's not provided-- that really, really bothers me.

Sorry, my mother tried to guilt trip me yesterday when I said I didn't want to go on a two hour drive to a flea market with her, so I'm very sensitive at the moment

But, anyways -- this is not normal. Your instincts are right. It sounds like you are handling them pretty well. It might have been better to tell them the truth about why you didn't want to visit on July 4th, but you may have reasons for lying. At that age, if I told my mother that I was spending the 4th with friends, she would have invited herself along!

I would figure out how much contact you want, separate from how guilty they make you feel. You don't have to call them every week or turn up for every minor holiday. If you want to, fine. If you don't, fine. They are obviously not going to cut the strings, so it will be up to you.