@mary- I would have to agree with MonoV on the beating yourself up part. Additionally, you mentioned that you experienced some insecurity and anxiety when a new woman was introduced. To me, that may indicate that you might need to take some time to focus on building self. That's not to say that people in multipartner relationships do not experience tinges of various emotions; however, I do believe that we develop a different, more introspective way of processing these instances that allow us to reflect on identifying the foundation of the trigger and working towards remedying that.
Also, maybe you should evaluate why you originally encouraged a poly relationship? That can also help you identify if it truly what you want or if you are seeking the satisfaction of your mate moreso.
Please do not beat yourself up and also do not allow yourself to remain available to your exe until you have found some peace in it. Communication that harps on comparing mates or keeps 'hope alive' is not healthy if it isn't genuine. *hugs*