Mariposas en el pecho literally translates to "butterflies in the chest." This phrase is a beautiful and common idiom in Spanish, similar to the English "butterflies in my stomach."
In the context of the song, Manuel Medrano uses it to express the intense, fluttering feeling of excitement and nervousness that love brings. It's a vivid and romantic way to describe being deeply smitten and feeling alive because of someone's presence.
Manuel Medrano, a Colombian artist, turns falling in love into a sweet, practical promise. The singer wants to love this person for life, kiss them every morning, and take care of everyday things such as coffee and food. He imagines them flying together under the sun, then admits, “el sueño se me ha cumplido” [the dream has come true] because this person is already beside him. The central image, “mariposas en el pecho” [butterflies in my chest], is a Spanish way to describe the excited, nervous feeling of being in love. This person has given color to his “black and white” world and is so special that he would go with them “to the end of the universe.”
The song gets especially warm and playful when he asks the person to stay and says he wants their pain, magic, and warmth close to him. The final images bring love down from the galaxies to a very Colombian meal: Cartagena, coconut rice, mojarra, patacón, shrimp, and pink sauce. That mix is part of the charm. He can imagine flying across seas and galaxies, yet he is also dreaming about cooking dinner together. The funny, affectionate conclusion is “tú eres la única que hace que me den cosquillas el amor” [you are the only one who makes love tickle me], a charming way to say this person gives him a special, fizzy kind of happiness.