I would sit down and have a serious talk with him. Find out what his motivations are exactly. Also how is he sabatoging you? Is it a matter of bringing off limit foods home all the time, constant coments, or just stating you look fine the way you are? This WOL is not only about weight, it's also about being as healthy as possible. You need to remind him that your health is important, and you have a responsibility to make sure you ar ein the best shape possible, and to control things like cholesterol.

You are already well within a healthy weight for your height though. Could he be concerned you are trying to push your weight to low and sacrifice health for it? You may want to get your body fat tested and see if a goal of 120 pounds is even possible without sacrificing lean weight such as muscle and bone density. What may be a better goal would be to get into shape and tone up your body without worrying about weight. That could be something you and SO enjoy together. Take couple or family walks, or spot each other in the gym. That's how my SO and I started getting together Now I can't drag him to the gym :P