Dissolve each box of red jello into separate plastic containers using only 1 cup of boiling water for each box. Mix well to ensure combined. Cool down and cover with plastic wrap.
Chill overnight or at least 24 hours to set.
The next day in a bowl add your gelatin and pour two cups of boiling water over top to bloom the gelatin. Stir well.
Let cool a little and stir in sweetened condensed milk until cool to touch.
Cut the red jello into small similar shaped cubes or use a heart shaped cookie cutter to create heart shapes.
Carefully place in a 9x11 casserole dish. Pour cooled gelatin and milk mixture over red jello, cover with plastic wrap and chill over night.
Using a flat thin small knife or spatula, carefully cut around the side of the casserole dish to loosen sides. Slide spatula along bottom and remove pieces carefully.
Best served immediately however it will keep in your refrigerator for a day or two.