Does he miss you, well he has his Mom to complain to now. You know, the way he treated you is really not right, please keep that uppermost in your mind.
Being confined right now is really awful for you. Do try to get out as much as possible though, walks outside (keep your distance
Whatever you can do that makes you feel free and uplifts your spirits a bit.
What is your plan? Do you plan on getting a place of your own, does your house need to be sold first or anything? Why is he sitting in your place while you are at your parents, can he not go live with his Mom? Sorry if you have gone over these details before, I can't remember.
Her opening your mail is a huge indicator of what she is like, total lack of respect.
I'm so glad you are not having to work side by side with her anymore.
Does he miss you? In his own way probably. However, that doesn't change anything. She says he is sober, I wouldn't bet any money on that.
Keep doing what you are doing but please take time for yourself and taking care of yourself, go for those walks, listen to your favourite music or watch your favourite programs, read what you like to read, eat what you like to eat!