Thank you for clarifying that your daughters are in their teens, that is an important part of this picture. I think that there are several other important parts to this picture that we cannot see yet. Could you describe what you are feeling for each of the women in your life? You said that this might just be limerence (I would assume with your GF), which seems to say that you are very invested in that relationship. You also say that leaving these relationships would be like cutting off a gangrenous limb, which seems to imply that staying would somehow kill you inside (perhaps kill off this new you?). I am a bit confused about what you actually feel for each woman, and that is something we would need to know to be able to help you think through things more fully.
Another thing that would help is to know what you think would be different / better without these women in your life. Are you afraid of going back into your old dependent ways? Do you just not see the point of the relationships now that you no longer have the deep needs for external validation? Are you looking for more freedom / experience? Ok, I will stop putting words in your mouth, but if we don't know what your needs are we will have a hard time offering useful advice.
That being said, I will offer what thoughts I can with the information I have. One of the freeing things about poly is that you are not constrained to the typical relationship roles and dynamics. If you choose to stay with your wife, you can do so on different terms than you have had in the past. As she is the mother of your children, you will continue to have a relationship of some form with her for the rest of your life, whether that relationship is occational contact at weddings, etc, or as live-together friends and partners, or any number of styles of romantic relationships. It would likely be a painful process to seperate completely, so I would recommend you look at ways you could have your needs met by re-negotiating your boundaries. You may find that she is willing to give you the space you need to disover yourself without cutting ties completely.
I wish you well,