The first question is whether he is receiving disability (based upon work history and "credits") or SSI (based upon financial need). If he is receiving disability (SSD), then he can win the lottery and continue receiving benefits as long as he is "disabled" and cannot work. If he receives SSI payments, your income may reduce or completely offset the SSI payments. So, your first step is to determine under which Social Security program he is receiving those payments.
Hope that helps and good luck.
Too little detail is given. Threshhold amounts, time frames etc... are some of the details you should go over with an attorney you hire on this complex matter. This is an online forum for general legal information, not a place to obtain legal advice for complex legal problems.
You have not furnished enough information for a definitive answer. If your boyfriend had an attorney help him with secure his disability, you can ask that question of the attorney. Otherwise, a simple call or in person consultation, providing answers to all questions asked of an attorney who specializes in this field of law should result in a more certain answer.
Yes, he can lose benefits upon marriage if he is receiving benefits as a "disabled adult child." Go to www.ssa.gov for answers to many questions. You should seek a consultation with a Social Security attorney in order to provide all details and understand your situation best.
This response is based on the limited facts presented and is not intended to substitute for direct legal advice, nor is it intended to establish an attorney-client relationship. It is intended to direct you to issues which you may desire to explore further.