I'm betting she's either a fetishist and got pissed that her fatty got weight loss surgery and is now losing weight, or she was just your run of the mill enabler and was banking on him having an early death where she'd make off with his life insurance. Which again, if he's finally losing weight means he probably won't die as soon. Now that her meal ticket isn't eating as many meals, she's given up all pretense of loving him and is moving onto the next thing.