WORRY! In our opinion she is cheating with your knowledge.
Your first question was – is this a problem. You stated several times that you were not comfortable with this. I (Mr.) have learned long ago that if it is real to you it should be real to her, where she feels so or not. This has to be addressed – and soon! You are not comfortable with her activity – end of story.
Second, if I read it correctly your fantasy was to WATCH her. This is not your fantasy; she is getting something from these guys that she is longing for. It could be several things, attention, and the idea of being desired by other men or a myriad of other possibilities.
And no, this is not normal….