Again, that is Identity Theft, an entirely different issue. Someone using my SSN for work just means, to me, that I made even more money that year. That's all. It doesn't harm me it screws up Social Security.
You have no way of knowing if he will use it just for work or to gain credit and wreck your credit history, which would be a concern for you if you were a grown up, but even if it is just for work, when he or his family use his employer's health plan, the treatments and medications they receive will be reported to the MIB under your SS#, potentially using up any annual or lifetime capped benefits you may later need. In addition, since all major insurers use the MIB to assess risk, when you apply for life, health or disability insurance, whether or not you get it and at what rate will be partly determined by his health history.
Further, if he becomes disable or decides to take early retirement, he will receive SS benefits that will be taken from your account.
If you had been out in the world on your own you would already understand how all of this would effect you and your family.
Your posts sound like you might have been stupid enough to have given some one permission to use your SS# and if you have, if he is caught you will also face criminal prosecution for all of these acts of fraud you and he committed.