Have a movie marathon
Either alone or with another single friend. Get all the movies you can, and be sure to avoid romantic ones. Go for as much blood, fun or horror that you can find and watch as many of them as you can. Or even binge-watch a whole season of your favorite series.
In the end, your best bet is to probably ignore the holiday completely. If you just treat it like any other day, you can quickly see that it’s not so bad and you don’t have to feel inadequate that you’re not a part of a couple. Just call it February the 14th, without any other meaning, and treat it like it deserves: like any other day of the year.