Congratulations on your enormous weight loss. That's more than 20 percent of your body mass! Anyone would be proud of that. I think the key phrase in your post is "I' have given up on myself." Not to get too pop-psych, but that sentence is full of context, indicating that you have a certain bent toward self-destruction that got you to 500 pounds in the first place, and will fight to gain superiority again. But you know better. You can beat it.
If you can give up on something, you can do the opposite--advocate and fight for yourself. It's a struggle but I've done it, so I know it can be done.
I found a book that simply took negatives and turned them into positives by allowing the argument to happen. If I thought, "I'm so ugly," I immediately shouted, internally, "I'm so beautiful!" I know it sounds kind of silly, but the thing is, you have a habitual consciousness and a manipulatible subconsciousness. When the negative habit tries to knock you down, stop. Immedicately say the opposite, and keep saying it until the negative quiets down. It's kind of like a form of self-hypnosis.
Another way to think of it is to ask yourself the simplest question: Why do I do this to myself? Why don't I decide to be a beautiful fairy princess who has magic powers and is filled with love? Why negative when there's so much positive available? Look at what you did already! Don't you believe you can do that again? If you can regain weight, you can surely re-lose weight.
I know as I grew up I was constantly criticized and told I was ugly. The first time I tried to commit suicide I was 17. I struggled with self-destruction for many years. But people and ideas and therapies came along and I was drawn like a magnet.. My life changed, and little by little I was able to take in positives.
If all this therapeutic self-care doesn't work, then just stop eating so much. Period. If you want to quit smoking, you do it by not smoking cigarettes. Duh. Simple. I know the agony, but you just have to fight. Swap your current pain for the pain of fighting toward a goal. Part of fighting isn't violence: it's love.