If he's trying to sabotage you then that's a problem. You need to talk to him about it and find out why- he shouldn't try to deceive you into doing things (like eating food not on your diet) against your will. In fact, if you think he finds you less attractive you should talk to him, period.
Actually, I'll emphasise this. If he's trying to sabotage you then he's not supportive, in fact the very opposite.
My boyfriend's very good about it. He says he'd love me at any size (he admits that if I got too big I'd be less attractive, but he says I've never been that big that he's known of; and that if I got too thin and I didn't listen to him he'd drag me to the kebab shop and force me to eat- I agree with him on this) and my happiness is more important than his preferences. We're very open about it and I've asked him to tell me if he thinks my habits are unhealthy or my goals are unrealistic (so far, the only thing he's unhappy about is that I refuse to eat out because I can't calorie count it).
Actually, my only real problem with my boyfriend and weight loss is that he's not putting enough effort into his own weight loss- his is a health concern.