You’re basing your relationship with your family and, I presume, your partner on a lie. You will live the rest of your life with that lie and the possibility of being find out. I suggest you tell your family how much you are struggling and give them the choice to support you or to not. If they do, you’ve strengthened your relationship. If they don’t – and the fact you don’t think they will is a fair predictor of that – then you know where you stand and you should consider moving on.
Your body, your choice and they should respect that. But the same goes for their relationship with you and you’re denying them a free choice.