Hi Sparklepop, I enjoy your posts and I remember your previous/ongoing issues.
My experiences don't really qualify me to offer much advice to you, but one thing jumped out at me: meeting your girlfriend's lovers / potential lovers online is NOT working.
Would it be possible to stop doing that? Do you really need to chat with these guys at all? Why do you need to interact with them or "meet" them in any way? Could you wait to meet them in person at a later time, when and if they become more serious with your girlfriend?
I understand that you want to get to know them and to make sure they respect and understand your relationship with your girlfriend, but it sounds like you are thinking of these online chats as a formal meeting of metamours, while both your girlfriend and the guys are taking it less seriously, perhaps just thinking of it as a casual flirting/sexting chat.
For what it's worth, I don't think your girlfriend's being very fair to you.
BUT, I am also wondering if you could consider a totally different approach to poly: a more autonomous approach. Would it be possible to regard your GF as a totally separate entity, able to date people completely separately from you, with no restrictions on her dating life? (You get the same autonomy for yourself, of course). I know that you are trying to do get to that point, and that you have very reasonable limits that your GF doesn't seem capable of respecting, but I'm wondering if it would be possible for you to reevaluate your entire approach?
It seems to me that your GF could date as many men as she likes, spank them as often as she likes, etc, and at the end of the day she will still be in a committed relationship with you.
I sympathize with your desire that she not date during the first week or so of your separation when you go back to the UK. But I think you are missing the point that she is a very different person from you with very different needs and (maybe) a very different approach to sex & dating. When you go back to the UK, you miss her so much you can't even contemplate going out to date a bunch of new people. You think, "I'm away from my girlfriend and I'm sad." Meanwhile, I suspect that she misses you just as much as you miss her, but that her needs & approach are so different that her thinking is more like, "My girlfriend's gone...now I have a lot more free time, and now I need a lot more sex than I'm getting, so I better go out and date some new people!"
Would it be possible to step back and say, "It's none of my business what she's doing when I'm not around. I know she loves me, and I trust her." ?
I would, however, stand firm on the limit that she not sext with men while going to bed with you. (And don't make the mistake of blaming the men for "not respecting" you if they are sexting her...it's HER choice to text and HER responsibility to turn off her phone at bedtime.)
I don't know that a more autonomous approach would work for you, but it's worth thinking about. It would mean that both of you would have to learn to communicate LESS about some things (for example, she can decide if she needs to bring condoms on a date without your input!).
Single, straight, female, solo, non-monogamous.