What should I do?? TW

Hello guys. Im not quite sure if this is the right place to be posting this, so Im sorry if I have posted in the wrong place. But I need advice.. ive been quite sad for a long time due to a lot of reasons but Im quite confused about this one. When I was younger I was taken advantage of by my older cousin. I havent spoken to anyone about this before, this happened about 10-13 years ago and only happened once. I didnt think about it for years until about a year ago and I think about it a lot now. Im not sure if I should tell someone like my mum or my therapist or just work on it by myself and push it away since it only happened once? Im embarrassed to tell anyone just in case its not serious enough or just a silly kids thing.. any advice on this would honestly be amazing.
thank you so much in advance also