Tough situation, sorry to hear it.
I'd start with your man; he's the one you need to be able to talk to in future years. Find out if this is typical behavior for his mom, and if she really means it when she has an outburst like this. Establish with him how you should deal with her, or if he should be the one to do it.
In fact, I think he is the one who needs to deal with it.
(My wife has been a
big help in making me deal with my mom more effectively.
)