Any time one partner makes big changes the other one is going to feel insecure. You dropped a bunch of weight, started a whole new exercise lifestyle - I'll bet it required a big chunk of time away from her. Maybe she feels threatened? Like that you are having an affair or are thinking of leaving her?

Any time I feel insecure, what I want is to be validated and to be told that things are okay, and that there is nothing to worry about and that my partner still loves me and is not thinking about leaving. I would be very insecure if my partner suddenly did a 180* in his habits and appearance. It's unnerving. Especially if I were over weight like your wife. Add to that a bunch of arguing and it's bound to be tense.