Should I tell my mom

I was sexually assaulted about a year and a half ago and never told my parents for several reasons. Some of the main reasons being I didn’t want to ruin my birthday dinner for everyone else, I thought if I waited a few days to tell them they wouldn’t believe me because why wouldn’t I do something there and then, and because I feel like there’s nothing they can do and this news will do nothing but upset them. One of my friends believes I should tell my mom but I think it’ll just hurt her and since very few people know about it I thought I’d come here and ask your opinions.