in-laws or "sorta inlaws" as Unhappy Tummy Steph calls them can really cause stress. I had awful strife with my sorta MIL during the summer when BF was in hospital and I was doing the caring (she was doing the irritating!) we are friends again. I just think of my Mom and the things she would probably say to my brothers' gfs (they are all single right now) and she wouldn't really mean it.
That said when sorta MIL does ANYTHING to me I rant about it!
You are sick and if living there is causing you extra stress then you should get out of there. You need to look after No1 to make sure that you are well.
BF will understand, they are pretty good at that. Just take my advice and don't criticise his Mom too much to him, its not fair to ask him to take sides as he is duty bound to defend her in some way and men think that when we tell them things that they must come up with solutions as opposed to just listen to us vent! (Guess who read "Men are from Mars"...!)