Re: my fiance is cheating on me??
Sadly...our mothers and fathers are sometimes the last people to understand how hard the relationship is becoming. Your mother is thinking of your status as a girl with a broken engagement, who will marry you now, the badnami in the khandan, the reactions, rumors and your prospects of finding another man scared her into reacting the way she did. Its okay...somewhere in that reaction...there really is love. Trust me.
Now, the meshing of personal things like Collide mentioned is natural...very natural. I dont think there is anything wrong with having passwords to email accounts but it has never occured to me to ask him for his.
My observation is simply this: you dont trust him, you already mentioned it might be a greencard thing, you've caught him doing this before and most importantly he seems to have an excuse ready for everything.
Why do you care about a guy who is so careless about your feelings? Do you think it will get better once you marry him?