social security benefits and marriage

Hello. I have been with my boyfriend for three years. We're not engaged but we do want a future with each other. I know he is the one I want to marry (in the future) and he feels the same but this is something we would want in a few more years. Not now as we're both only 25 but a few years down the line we will consider this. Our relationship is strong and we already have a gut feeling that we will have a future. But recently he had to apply for disability benefits and social security. Reasons being, he has severe degenerated disc disease and stenosis. Pretty much that is severe lower back pain that will not go away. He's on heavy narcotics that make the pain tolerable and he can function normal when he's on them and does not abuse them. But holding a normal job is very difficult for him. He recently applied for disability and we hope for the best but we were recently told that if you get disability or social security benefits from the government then you could never legally be married and if you're already married you have to get divorced or you will be denied. I can't find info online about this. Does anyone know if this is true?