As I've been getting to know my girlfriend, we've been sharing more about our pasts and habits. I'm writing you today about one of them.
I don't like the idea of other people looking at my girlfriend naked. She's very comfortable with that, but I'm not. Apparently she doesn't have a problem changing openly, like when she shares a tent with friends while camping.
She has a very nice body, and I would like to be the only one to see it. I love her and I don't want her to be naked around other guys. It's just not right for other guys to see her sweet body...it's just not right. Am I being selfish?
I know a few people like your girlfriend, who don't really care who sees a stray body part while she's changing into a bathing suit. Those people tend to do this around close friends of the same sex.
You didn't describe your girlfriend as a professional stripper, nor as an exhibitionist. Thrusting those probabilities aside, I think it boils down to your girlfriend feeling comfortable around her friends regardless of of their gender.
But of course, you wouldn't like this. Being naked immediately means sex or an orgy, doesn't it? In your eyes, her body is such a peach that someone else would immediately take a bite if they saw it. That's why no one is ever allowed to see it again. She's your dessert, no one else's.
Since that's not the way she sees it, she's probably not going to listen to you if you ask her to never undress in a situation where people are undressing unless it's with you. Some people are just not supermodest; usually that Puritanical trait goes out of favor in locker rooms as you get older. You should see the number of old biddies who are naked at the Y! I'm certain their husbands or partners aren't complaining about that.
I don't think your feelings are selfish so much as kind of normal, but this is one of those situations where your girlfriend probably won't feel the same way as you do. Take that information for what you will.