Today is a new day and I'm sorry you have a headache. Could it be that the headache is stress related? You've had a lot going on at work and at home this week.
I am going to suggest that you try not to over analyze every word or action he takes. The more you try to do this, the more upset and annoyed you will get. Right now, he's a very unhappy man and he thinks that the rainbow across the street is going to provide him his freedom and make his life easier. Maybe it will and maybe it won't...but you can't control the outcome for him...but you can control your outcome and face anything that is thrown your way.
As for your MIL, I would limit my contact w/her. She may be fishing for info and then again maybe not...but whatever the reason...limit the contact and when she asks for help again w/a pet, refer her to someone else or another web page on the interest...but get yourself out of the loop w/her for the time being. I know you want to help..but right now, the only person that needs your assistance is you. Could your MIL be trying to connect w/you because of what she has on FB? Maybe she wants to fish to see if you've seen her postings. Whatever the reason, distance yourself from her as much as possible. Blood is thicker than water.
As for FB, I wouldn't be on that unless it was to connect w/your side of the family and friends. Otherwise, radio silence for a while.
From this day forward, I would not say another word to your h about you needing your space...actions speak louder than words. Just don't respond to his text messages...silence is golden. He fired you as a wife and companion. Time for him to man up and do the necessary work.
Tomorrow...hold your head up, back straight, and dress nicely. You want to do these things to bring that confidence level up and let it shine for all to see. Keep your expectations at zero at all times. KK, you can do this. Once he's gotten his stuff, there should be no reason and/or excuse for him to return there. If he contacts you after removing all of his stuff, then just say when I have time, I'll look for it. Nothing says you have to jump through hoops for him.
It may take a long time before the euphoria of his new life to come to an end, but no matter what happens...you will be okay. You are a strong and intelligent woman and you will get through this.
Try to have a good day and stay safe. Hope you feel better soon.
Sit quietly, the answers will reveal themselves when you least expect them to. The past is gone, the present is a gift and you need to focus on today, allow the future to reveal itself when it is ready.