Should i be mad at my girlfriend for hideing a secert from me for a while now?

well me and my girlfrind have been goin out for 10 months now.and she kept a big lie from me for a while.she told me everything she has every done with aother guy and she tole me that a family friend (a 19 year old guy that her stepsister knew and her dad to)well that he touched her down there and soi was upset and mad about it.so i ask her a few months later when she told me and we started talkin abou it more and she said it was true an everything.so after i kew that itold he i didnt want her talkin to him anymore aftter that.welli just found out that the whole thing was a lie and notin happen.an thenshe told me that she till taked to him eve after i tld her not to.what should ido?