I had to take that walk at the beginning of the year. My husband had to do it for the first time a few weeks ago on one ride at Magic Mountain.
If it means anything...I was able to get on the rides at one of the local amusement parks when I was your weight...of course there were a few that were a bit tight still, and my husband is well over your weight and he fits on everything except that one ride. But I also realize that people carry their weight differently.
You can try a few things, check online...all of our parks here have a section online that explains what size the rides are for. Here it is 225 lbs or size 18-20. I am obviously more than 225 lbs but I wear a 18-20. Or like another poster suggested, call ahead. There are also usually a few seats on the rides that have bigger seats or belts. You can discreetly ask the ride operator when you get to the front.
Have the hubby change his mind. Suggest something more romantic, private whatever. Or just be honest with him. My husband is like yours, he does not notice bad things about me at all. He barely notices bad things about himself. It is great. Super supportive...until it is not and it becomes enabling. Just sit the hubs down, ask him to really LOOK at you and recognize that there is an issue, and while he may not be able to understand it, ask that he understand how you feel, and that you are not comfortable right now with going to an amusement park that may cause you embarrassment. If your husband is as much like mine as I suspect, he will not want to in any way be the cause of your discomfort or embarrassment and will be OK with changing plans.
You can always use the Cedar Point trip as a reward for a mini goal