I'll be honest. I am someone who IS in a relationship, and I AM happy. However, I am fully aware that I don't need romance in order to be happy or even to have fun on Valentine's Day.
A lot of people, especially around this time of year, want a relationship just to get into a relationship. Don't do this! Trust me, I completely understand that there is pressure and a lot of emphasis on romance. However, neither you or nor your partner will be happy if you try to initiate a romance out of loneliness and nothing else.
If you're going to be single on Valentine's Day or at any other time, don't stress. Hang out with your family or your friends! They make you happy, correct? Yes, it is nice to have a romantic partner in your life, but there are other people to love and other people who love you.
You may not realize it at first, but platonic and familial love are actually quite underrated in today's society!
That's not to say you shouldn't want a relationship, or ask someone out, or say yes if/when someone asks you out. It just shouldn't be your first priority. You can be just as happy single as you can be in a relationship. It's just a matter of letting yourself be happy and finding the right group of friends!
The less you stress about trying to find a significant other, the better you'll feel in the long run, even if being single hurts or feels lonely right now. There's absolutely no shame in not having a partner. Buy some chocolates for yourself and for your friends, and call it a day. You already have all of the love that you need.