OK, so the two of you are just beginning this new journey. It sounds like while you both state you wish to work on the M, that the work hasn't really begun, yet.
So rather than fear what MIGHT happen, consider this the acid test. If your M is to succeed, this is where it begins. Your practice and effort, just like all the DBing you've done to date, needs to be real and permanent.
Nothing that YOU do should be done as a ploy or concession as a "one off". No "half in" type of stuff.
Sure, it's scary to be that vulnerable. The payoff though... can not be put into words. And if it doesn't work out, it certainly can't hurt any worse than it did at BD. In fact, you have the tools now to work through that, if things DON'T work out.
So... if you were brutally honest... do you fear that YOU won't put in 100%? Or do you fear SHE won't put in 100%?