You are definitely not overreacting. What i have experienced is that you only find out the true intentions of people when you start living with them. One possible solution for you and your husband during discussions is to just go to your room close the door and have the discussion in private. or go out for a drive and discuss it with him there.
Having it in front of your Mother in Law will not give you any benefit.
Liking the ex is definitely strange. Your mother in law is facing past bias. Since she's living with you, all your limitations are being amplified to her and all that ex girls good qualities are also being amplified.
I think for your sake the best case scenario is to move out with your husband or find a job,
we can talk more so hit me up. But do remember, it is your life first and foremost so you have to think about yourself as well