I'm so sorry to hear you are going thru all of this, at a time when you should be on top of the world.
I to had a FMIL much like you are dealing with. She is now my Ex-MIL...Thank God!
You need to have another talk with your FH. Once your married this woman will not just GO AWAY! My run in's with my Ex-MIL just intensified and after the children were born it became even worse. My advice to you is if you think your FH is unsure and he is not totally committed to you and your marriage together...put the brakes on...There is no place in your relationship for his committment to his mother over his wife.
This woman reeks of my ex-MIL. She did the unthinkable...
Be true to yourself first, and your FH 2nd. This woman doesn't deserve the admiration or respect of either of you.