Hi!
To find stock photos for Valentine's Day, I often use a few trusted platforms:
Depositphotos: A great resource with a lot of free high quality photos. Here you can find beautiful and creative images perfect for the holiday. Here's a link to the theme you want
https://depositphotos.com/photos/valentine's-day.html.
Shutterstock: Although this is a paid platform, it offers a huge variety of professional photos that can be suitable for everything from social media to advertising campaigns.
Pexels: Another free resource with a large selection of romantic photos. They often have very beautiful and touching images.