Have you talked to him about it? Does he shrug it off? If he won't take it seriously, you've got to just put your foot down. Tell him to stop bringing junk into the house, you're sick of it and you will not tolerate it in your home. Remind him that he had GBS so he NEEDS to eat well, plus you're trying to lose weight. It's not fair of him, he needs to be supporting you. It's like putting cartons of cigarettes in front of someone trying to quit. Then of course you have to worry about him buying food while he's out and just eating there. Have you (or he) thought about therapy?
My partner would try to bring in junk when I was trying to improve our eating. What I finally did was everytime he brought crap into the house I gave it away to someoen else. Once he realised that if he kept it up, he'd waste all of his spending money on food he wasn't eating he stopped. And I told him we'd go on WW together and he'd probably love it. And he does. Why? Because he can still eat his favourite foods in moderation, he's learning portion control, and he gets a lot of points
But yeah, try talking to him first for sure. If he doesn't listen/shrugs you off/doesn't take you seriously I'd honestly just chuck all the stuff he buys into the garbage and pour Lysol on it explaining to him that you can't have that kind of temptation around and any food you find in the car or house will be treated the same way so he might as well stop wasting money.
Also, sit down with him and make a list of your guilty pleasure foods and try finding low point recipes so you can still have them. My partner and I both looove pizza and cheese sticks. Now we make homemade pizza with skim cheese and wheat crust, and I make the bread crumb cheese sticks (the recipe is in the WW recipe section of this board). Much healthier/cheaper in points AND we get to eat more.