I recently stumbled across the website cardboardlove.com and I've become somewhat addicted. Both innocent and romantic the charming little notes left by the creator for their partner are simple and so endearing . On making the website they say "In general, I am a pretty negative person. This project has been a chance for me to focus on the positive for a change." - a mantra that highly resonates with yours truly.
Here are some of my favourites from the website -