Toxic MIL not letting go?... lol pls help

Hey ladies I need some advice on how to deal with this...

(Together for 4 years just got engaged, we’ve lived at his parents house for 2 1/2 years - his dad passed away and his brother lives 6 hrs away. It’s just the three of us) we live in a two story house probably close to 2500 sqft. The entire half of the upstairs is the master suite and the other half has 3 bedrooms and a bathroom. MIL has her master suite and we have our bedroom, bathroom, living room and a guest room!!! To set the scene lol

I got home from work last night and I hear MIL running across our hall upstairs and then the spare bedroom (our spare bedroom) light turns on. I walk up to see she took off the sheets I made that morning and was “re-making the bed” , I asked her what she was doing and which I semi-ignored. I texted my man to let him know what I think I heard but don’t jump when you get home let’s talk first. He was pissed.

He gets home from work, goes to his closet, turns to me and goes “you were right”. All his work clothes were hung up!!!!! Which means she WENT THROUGH OUR DIRTY LAUNDRY AND FOUND THEM ALLL!!!!!!!!

she was clearly in our room and tried to hide it and lied to my face about it.. I told him to know bring it up right now, talk to her tomorrow.

So they talk in the morning she says a few quotable things like “I guess I just need to get used to half loads” I HAVE BEEN TAKING CARE OF MY MAN FOR 2 1/2 YEARS. and “I’m sorry that a frustrate you guys soooo much” like that the fuck.

Me and him spent a good time today texting over this as he feels it’s impossible to make me happy in this situation.... it’s like you can’t just say “man up and talk to her!!!” Anymore these days...

I am not willing to lose the love of my life over this petty shit but he can’t see any of it because it’s his fucking mother.... do I walk away?? Has anyone been in situation like this, i obviously don’t want him to hate her but she has been playing him as a fool his entire life!!

We are planning on moving out ASAP but obviously we aren’t made of money.. we work good jobs and are working our way through school for better jobs. We are really trying but this is putting a major toll on our relationship