I have played the loving and remorseful husband and have tried to do what I can to work with her. I want to make things better for BS, but otherwise my heart does feel in it.
Stop playing parts. You have been uncertain about the M since before you got into it. IMHO this may be contributing to your ambivalence.
I was concerned I did not love her enough.
This is most likely a projection. There is a good chance that you were really feeling that she did not love the real you enough. Which is most likely the case if you have only been playing the part for the duration of your M
So down to my questions.
1.you considered calling off the wedding, why didn't you?
2. you considered getting an annulment, why did't you?
3. have you ever loved her?
4. have you told her the complete truth? not holding anything back?
observations:
1. you are a couple weeks out from DDay, this is way too soon to tell anything. give it at least 4-6 months of NC with the AP. Make sure your head is clear. And that you make a thoughtful decision. This is going to be one of the biggest decisions of your life.
2. You were excited about the thought of D. totally normal reaction to not wanting to take accountability for your actions and the destruction that they have caused.
3. You want to make things better for your BS, but your heart currently isn't in it. I can promise you that if that continues, the only way to make things better for your BS would be to D and to do it amicably. Why would the best thing for your BS be for you to "Put on a show" No the best for her is to be fully loved, and if after much time you cannot give that to her. Than you should set her free to get that somewhere else.
4. You need to fix what is broken in you. Fix what made this okay for you. Because staying with your BS or moving on doesn't matter there. You have to make yourself a safe partner.
5. the statistics are such that 50% percent of first marriages, 67% of second, and 73% of third marriages end in divorce. So leaving for an AP does not look like good odds. remember anybody that would not hold your M with your BS sacred. Would not hold a M sacred with you. And if you are thinking you will not be a statistic, the reality is you stepped out. So you are already a statistic.
6. Your ambivalence does sound like a defense mechanism to me. A way to make it not hurt as bad if your BS decides to go that way.