It's the fact that they asked her for nudes. Not that she talks to some guys...

There's a huge difference between not wanting your SO to have friends and not wanting them talking to people who obviously want to have sex with them.

While I get that it makes OP uncomfortable, I don't think anyone ever has the right to prevent their SO from talking to someone. I mean, sure, OP can explain why it weirds him out, and ask why she would even want to keep talking to those guys, but it's up to the girlfriend to decide what she does with that. If OP literally told her to stop talking to them, I understand that she wanted to break up.

#26 I take it you'd be fine with your partner sending nudes to almost ten people then? Because hey, you don't have the right to tell them not to, right?

As a matter of fact, yes, I would be fine with that, although I would probably advise him to take care with sending nudes as you never know where they might end up. But that's my personal opinion, and I get that everyone has a different comfort level with regards to this type of thing. That's why it's important to discuss boundaries when starting a relationship. If OP is uncomfortable with his partner talking to people who are interested in her in a sexual way, that is definitely something to discuss with her. However, it sounds like OP simply told her she needs to stop talking to them, which seems controlling and unhealthy to me. There is a big difference between "you do this thing that I'm uncomfortable with, can we talk about that and see if we can find a solution that works for us both?" and "you do this thing that I'm uncomfortable with, and I've decided on my own that you need to stop doing it".

That would be fine if the relationship was open, but it's clearly not.

#37 is missing the point. OP didn't TELL her to stop. He said he ASKED her. There is a very big difference between those two things.

Nothing indicates that she is disloyal. Just that people ask her for nudes.

#22 And she did nothing to discourage them, AND kept talking to them all. Most people in a normal, stable relationship would call that a "warning sign".

I got stuck on that exact phrase for a similar reason.