How to tell my mom that I’ve been molested?

So I recently told my boyfriend of 4 years that my father molested me when I was 12, for about 2 months straight. I was so scared as I’ve never told ANYBODY or even said it out loud.

Well now my boyfriend thinks that my mother should know and he really wants me to tell her. I really want to but I just don’t know how to say it. It’s happened almost 10 years ago now, and I don’t want this to ruin my family. Has anyone been in this position? How do you tell your mom something like this? :(