Line a baking sheet with parchment paper and spread the popcorn out.
Add the butter to a small saucepan, and heat over low heat until melted.
Add the marshmallows, and continue heating, stirring often, until melted.
Drizzle melted marshmallow over the popcorn, then toss and spread out evenly again.
Melt the candy melts in pastry bags in 30 second increments. Knead the bag after each time. Once melted, cut the tip off the bag and drizzle over the popcorn.
Sprinkle the M&M's, then the heart sprinkles over the popcorn.
Place the baking sheet into the refrigerator for 20 minutes to allow everything to set.