Okay, so about a year ago my girlfriend sent nudes to some guy.

Which is understandable, because I've done crazy **** like that too, and she really regrets it, still cries about it, etc. etc.

When she sent pictures to the guy the guy showed basically a good handful of his friends at lunch last year (who are also my friends). He even sent it to one of my friends in my band, but he's had a girlfriend since then, so I don't think he actually got off on them.

They use to make fun of her body (No, she's not fat or anything, stuff like her nipples etc.)
But ever since I started dating her they apologized for it and my friend deleted the pictures. Hell, they even gave me a bit of advice when dealing with a situation like this.

I understand that it's the past, but it really bothers me how I can't hang out with a single friend group of mine with at least one or two people that have seen/know about her nudes. Please help.

Should I break up with her?

If you can't stand the heat, get out of the kitchen, so at least she can get a man who accepts her for who she is. I mean if you can't be a good boyfriend, then what's the point??

I am not without sympathy, but she has already paid for her past mistakes, and you acknowledge she regrets it. If you cannot get beyond this, well frankly you don't deserve her. This is a defining moment of YOUR character my friend, as your friends seem supportive, but its you that can't let go. If you allow this to be a wedge between you, and your girl, then you aren't relationship material yourself, are you.

Stop judging her for her past mistakes. Bury it, and have fun why don't cha. As you have said yourself, you have done some dumb crap too.

Totally your issue,

You have no problem sending them yourself it would appear. And no problem her doing it, if they were not people you know. Sounds sort of narrow minded to me.

To be honest with the G strings and the such women wear at the beach and stuff, there is not much left to see.

It is not like they are seeing it today, saw it since you were together. And most likely don't really remember it.
And they only saw a photo, not the real thing.

No!
Don't break up with her!
In this post, you didn't highlight any problems you have whatsoever with your girlfriend, so I'm assuming all is good with her.
Why end a perfectly good relationship because a couple of your friends have seen her naked? Who cares? At the end of the day, no ones body is perfect, and I actually think it's amazingly mature that your friends apologised to you for the comments they made once you started going out with her.
Even if some of the guys have secretly kept a picture of her and get off to it, how sad is that? You get the real thing while they have to make do with a picture.
If anything, you should just enjoy being with her, and be flattered that your mates might be getting off to the sight of your girlfriend.