Dichoso translates to "blissful" or "fortunate." It's a less common, more evocative word than simply saying "happy" or "lucky."
In the song, the singer uses it to describe how he felt after experiencing his first kiss: "Me sentà al hombre más dichoso por probar su boca" (I felt like the most blissful man for tasting her mouth). This word perfectly captures the intense, almost divine joy of that moment, making it a memorable and interesting choice.
Abraham Vazquez's "Ford 86" tells a story of young love and the regret that follows when it's lost. It starts with a sweet memory of being a child, falling in love, and spending all day talking, asking "cómo estás" [how are you] back and forth. The imagery of being in an old Ford 86, with the person on their lap, and feeling like "el hombre más dichoso por probar su boca" [the most fortunate man to taste her mouth] really sets a nostalgic scene.
But then, as often happens, "llega a tiras la rutina" [routine comes to tear it apart]. Fear of what others might say confused them both, and he admits, "de tonto me olvide que como ella muero" [like a fool I forgot that I die for her]. The song then shifts to his deep regret, wishing he could "buscarla, tocarle la puerta, irnos a la cama" [find her, knock on her door, go to bed]. He realizes it's too late, blaming himself: "yo fui ocuparé por no haberla valorado" [I was to blame for not having valued her]. Now he's "como un perro mojado" [like a wet dog], regretting everything and missing her kisses, unable to deny it. The final blow is the heartbreaking line, "el amor de mi vida se acaba de enamorar de otro" [the love of my life just fell in love with someone else].