You aren't F-ing up. You are doing your best during a difficult time. Your M does not hinge on the last 72 hours. But, it is time to find a healthier strategy.
Maybe it would help to put your energy into figuring out what a good talk for you would be -- what would you want to say and how would you want to say it? What boundaries would you communicate? What very few questions would you ask and how would you ask them? How would you react to possible things she may say (like the snooping thing) to keep things on course? How would you close the conversation?
You seem to be putting all your energy into stifling yourself. You keep telling yourself how bad the convo will be and how you don't have the resources to deal with it in the way you want to.
I think you should try telling yourself something else. "I am an incredibly strong and compassionate person who cares about myself, W, and our R. I am not perfect, but I can do my best to make this a valuable and caring conversation, which is what I need to do now to take care of myself and to take ownership of my own choices and their consequences. I can do a really great job at this, because I have grown so much. I like being like this and I want to keep it going. I will do my best while accepting that I am human. I will be caring and direct. I will not shout but I will not protect W from my pain. I will truly share myself with her and see what happens. I am strong enough to take this risk, I care enough to take this risk."
Maybe try writing down some talking points, even dialoguing with yourself and a pretend W on paper to get your thoughts straight, will help both prepare you for a real conversation and get you unstuck from where you have been since before the weekend.
Just work on the conversation and clarifying your own thoughts and desires. It really will help alot. Then, you can reassess and figure out if you are ready to talk to her or if you still want to wait.
Now, as to what kind of R you are in with W, that is really up to you. To me it seems as though you and she have both returned to some kind of dating R. You at least have. You either need to get what you need to make that an OK R for you to be in, or you need to step back out of the R so that your life is your business and her life is her business for awhile. I'm not sure that would be helpful to simply do that because you are afraid to talk to her though. If I were in your shoes, I'd want more information upon which to base such a decision.
