A friend of my husband and me touched my butt, but I'm not going to tell my husband.
Why wouldn't you tell your husband that your friend touched you like that?
I'm afraid once I tell him about it, he'll never look at me the same way again.
I understand that you do not want to tell your husband of what your friend did to you because your husband may never look at you the same way again. I think he would understand it was not your fault. Thus you should not hide things from your husband.
What if he blames me? He might divorce me.
If you hide it from him and he finds out later, he will feel betrayed and suspicious. That is much more likely to lead to divorce than an open, honest conversation about your friend making you uncomfortable. You didn't do anything wrong, so he has no reason to blame you.