Sarah... just hang in there. Don't take anything too personally.
I had issues with my stepmum over the years (god I must have given her grief)... but we are the absolute closest we could possibly be now. We live up the road from each other, and I can't get enough of her!

I really hope it's just a "thing" he's going through.
I really hope it's not anything that his mum is saying. (hows your relationship with her... could you discuss it with her?)

Good luck Sarah!