This is very interesting. In these two years, how often did you two see each other? In other words did you see each other enough for you to see any clues of anger, abuse, etc. And additionally how well do you get along with his mother? I would consider what his mother said but also question her intentions.
I am sorry but it seems odd that she waited for him to leave to bad mouth her own son. I am having difficulty understanding why a mother would do that.