When you show up on your own at a social function, you are unaccompanied, meaning you’ve got no date.
Use the word unaccompanied to describe someone who is "flying solo," meaning without a date or companion. You may have seen signs on doors of stores that say "No unaccompanied children allowed." This means kids need to have an adult with them, presumably because the store is full of breakables. In music, if you play or sing a solo, you are unaccompanied by other musicians or singers. If you perform that solo while at a party, without a date, then you’re unaccompanied on both levels.