Well, it's heat damage. Think about what heat can do to your skin if you lay out in the sun with no sunblock all day - it'll fry you. Now think about what it'll do if you put some sunblock on and then lay out in the sun all day - you'll still damage your skin. You may not get as fried, but you aren't going to walk away with no damage.
You can use protective products that coat your hair shaft and seal it off so that when you use flat irons and heat to straighten your hair, you can minimize the damage the heat (which is applied directly, as in, laid right on your hair, as I'm sure you know since you said you used to straighten your hair often) causes your hair, but you can not, NOT prevent the damage. There is no way to force your hair to go against it's natural instinct to curl, and not damage it.
On top of that, when you use products designed for straightening hair, those usually have alot of silicones in them - so you will need to use sulfate shampoo to get them out of your hair. Sulfates are drying and strip your hair, making your curls brittle and thirsty.
BTW, it absolutely IS possible to lose your curl if you straighten your hair too much. My mom's hair lost it's ability to curl because she constantly, daily flat-ironed it until it would no longer curl. This happened over a few years, but it did happen. She only got her curl back when she chopped all her hair off - and I mean boy-short. Luckily it looked cute, but her hair only started curling again when she got new growth. So yes, you can damage your hair from straightening so much that your hair will stop curling.
I don't think a summer of straightening will make your curls "go away" permanently, but I think you need to be aware that you could damage your hair more than you realize. And why should you have to wear your hair straight if you don't want to? It's your hair, not your mom's or your dad's. If you straighten it that much, your hair will not be happy, it'll be dry, and brittle and more prone to frizz. Your curls will not be bouncy and moisturized.
At the end of the day, wear it curly or wear it straight - but wear it the way YOU want to wear it, not the way your parents want you to