You know G in some ways I can relate to what M is going through. You have to remember that everyone leaves their marriage, has different views of what happened, and has been single for different periods of time. I agree with the above and it is so much more about him than you.
I have struggled on many different levels with the Dr. Even though our timelines are the same she wanted out of her marriage and was miserable while I was blind sided, still loved my XW and would have done anything to make it work. I also knew she wanted a LTR from the start and I wasn't messing with someone that was just going to be a 3 or 4 date fling.
I know the Dr. is a catch which is why I have not pulled back and have continued to stay the course getting more comfortable. It has nothing to do with her. She is an amazing woman, a giver, sweet and kind.
From what you have written on this board it doesn't sound like M has ever once mentioned or brought up ending things with you. Freaked out?? Maybe at times but that is much different than ending things.
I as well have been freaked out, scared, afraid to be vulnerable and commit but I have never been close to pulling the plug. I do think about my struggles from time to time but ultimately the Dr has a say in things as well. If she doesn't feel that I am giving to her and/or reciprocating based on her needs then she can easily end it as well.
And to the above it has to be from a place of strength. You are a catch, believe you are a catch, and realize that any man would be lucky to have you. It's not about if M thinks you are worth it......it's about if G thinks M is worth it.
If you do then give, love, receive, stay true to your boundaries and enjoy the R as it unfolds. Be patient, stay in the present and try not to read into anything.
TBH I have found the less I talk about the DR. on the board the less I analyze about the situation