Try to imagine if the situation were reversed. What if it had worked out great for you but she wasn't attracted to the guy. What would you want her to do?
It sounds like it may just be envy. I think you are right in not forcing yourself to be with them if you feel no desire. But there are always opportunities in the future. However, if you are not ready for it, then I think you should spend some time thinking about what is really bothering you and talk about it with your girlfriend.